add content on create new branch (#25)

episodes/09-conflict.md

@@ -40,6 +40,191 @@ different changes to each copy.  Version control helps us manage these
 [conflicts](../learners/reference.md#conflict) by giving us tools to
 [resolve](../learners/reference.md#resolve) overlapping changes.
 
+Before resolving conflicts, we'll review two features that a **good collaborator** puts in practice: Create branches and Atomic commits.
+
+## Create branches
+
+First, verify that you are working on the main branch:
+
+```bash
+$ git status
+```
+
+```output
+On branch main
+```
+
+The `git branch` command **creates** a branch of the name `newbranch`:
+
+```bash
+$ git branch newbranch
+```
+
+The `git checkout` command **switch** from the current branch (in this case, `main`) to the `newbranch`:
+
+```bash
+$ git checkout newbranch
+```
+
+```output
+Switched to branch 'newbranch'
+```
+
+Now, you can confirm that we are in `newbranch` using `git status`:
+
+```bash
+$ git status
+```
+
+```output
+On branch newbranch
+nothing to commit, working tree clean
+```
+
+Now, let's make an edit to the `sitrep.Rmd` file:
+
+```r
+usethis::edit_file("sitrep.Rmd")
+```
+
+```output
+Comparison of attack rates in different age groups
+This can identify priority groups for interventions
+Maps illustrate the spread and impact of outbreak
+Use packages listed in the CRAN Task View: Epidemiology
+```
+
+Add and commit this change to the local repository:
+
+```bash
+$ git add sitrep.Rmd
+$ git commit -m "Add edit in new branch"
+```
+
+```output
+[newbranch 60d5ff9] Add edit in new branch
+ 1 file changed, 1 insertion(+)
+```
+
+Push commit to the remote repository. NOTE: instead of `git push origin main`, we replace `main` with the name of the new branch:
+
+```bash
+$ git push origin newbranch
+```
+
+```output
+Enumerating objects: 5, done.
+Counting objects: 100% (5/5), done.
+Delta compression using up to 12 threads
+Compressing objects: 100% (3/3), done.
+Writing objects: 100% (3/3), 339 bytes | 169.00 KiB/s, done.
+Total 3 (delta 2), reused 0 (delta 0), pack-reused 0
+remote: Resolving deltas: 100% (2/2), completed with 2 local objects.
+remote:
+remote: Create a pull request for 'newbranch' on GitHub by visiting:
+remote:      https://github.com/vlad/cases/pull/new/newbranch
+remote:
+To https://github.com/vlad/cases.git
+ * [new branch]      newbranch -> newbranch
+```
+
+On GitHub, we get a notification to Create a **Pull Request**:
+
+![](fig/github-branch-pullrequest.png)
+
+In your local repository, you can leave your work parked for a while on that branch. To return to `main` (or to any other branch), you can use the same command to **switch** between branches:
+
+```bash
+$ git checkout main
+```
+
+```output
+Switched to branch 'main'
+Your branch is up to date with 'origin/main'.
+```
+
+## Atomic commits
+
+A good commit is also an __atomic commit__, like in the commit of the last challenge:
+
+```bash
+$ git add lab-test.jpg
+$ git add lab-site.jpg
+$ git commit -m "Use two images: test and site"
+```
+
+Commits should be ‘atomic’, meaning that they should do one simple thing and they should do it completely. ([The Turing Way Community](https://the-turing-way.netlify.app/reproducible-research/vcs/vcs-git-compare#good-practice)). Atomic commits prioritize one unit of change instead of the quantity of changes. 
+
+![Two related modified lines must be part of the same commit.](fig/git-rstudio-27.png)
+
+In Rstudio, the Review changes window has a button called “Stage chunk”. This helps to make atomic commits, even if you change a lot of lines in a single edit. You can either select them to make isolated commits or to unite them to be part of the same commit.
+
+![Two unrelated edits must be part of two isolated commits.](fig/git-rstudio-35.png)
+
+::::::::::::::::: checklist
+
+### Good practice
+
+A good atomic commit:
+
+- Includes more than one file that involves one unit of change. 
+
+- Isolate or includes multiple edited lines using the "Stage chunk" button in Rstudio.
+
+- Does not include all the files in one commit.
+
+:::::::::::::::::::::::::::
+
+## Group Challenge
+
+:::::::::::::::::::::::::::::::::::::::  challenge
+
+## A Typical Work Session
+
+You sit down at your computer to work on a shared project that is tracked in a
+remote Git repository. During your work session, you take the following
+actions, but not in this order:
+
+- *Make changes* by appending the number `100` to a text file `numbers.md`
+- *Update remote* repository to match the local repository
+- *Celebrate* your success with some fancy beverage(s)
+- *Update local* repository to match the remote repository
+- *Stage changes* to be committed
+- *Commit changes* to the local repository
+
+In what order should you perform these actions to minimize the chances of
+conflicts? Put the commands above in order in the *action* column of the table
+below. When you have the order right, see if you can write the corresponding
+commands in the *command* column. A few steps are populated to get you
+started.
+
+| order | action . . . . . . . . . . | command . . . . . . . . . .                   | 
+| ----- | -------------------------- | --------------------------------------------- |
+| 1     |                            |                                               | 
+| 2     |                            | `echo 100 >> numbers.md`                                              | 
+| 3     |                            |                                               | 
+| 4     |                            |                                               | 
+| 5     |                            |                                               | 
+| 6     | Celebrate!                 | `AFK`                                              | 
+
+:::::::::::::::  solution
+
+## Solution
+
+| order | action . . . . . .         | command . . . . . . . . . . . . . . . . . . . | 
+| ----- | -------------------------- | --------------------------------------------- |
+| 1     | Update local               | `git pull origin main`                                              | 
+| 2     | Make changes               | `echo 100 >> numbers.md`                                              | 
+| 3     | Stage changes              | `git add numbers.md`                                              | 
+| 4     | Commit changes             | `git commit -m "Add 100 to numbers.md"`                                              | 
+| 5     | Update remote              | `git push origin main`                                              | 
+| 6     | Celebrate!                 | `AFK`                                              | 
+
+:::::::::::::::::::::::::
+
+::::::::::::::::::::::::::::::::::::::::::::::::::
+
+
 ## Create a conflict
 
 To see how we can resolve conflicts, we must first create one.  The file