Make unzipping instructions platform-independent

Fix #484

Co-authored-by: Nathaniel D Porter <[email protected]>

learners/setup.md

@@ -12,8 +12,7 @@ You also need to download some files to follow this lesson:
 1. Make a new folder in your Desktop called `r-novice-inflammation`.
 2. Download [r-novice-inflammation-data.zip](data/r-novice-inflammation-data.zip)
   and move the file to this folder.
-3. If it's not unzipped yet, double-click on it to unzip it. You should end up
-  with a new folder called `data`.
+3. If it's not unzipped yet, unzip it. There should now be a folder called `data` in the `r-novice-inflammation` folder.
 4. You can access this folder from the Unix shell with:
 
 ```bash