add releasing procedure doc (#47)

This is mostly pull from the opentelemetry-proto repository. Linked issue #46

---------

Signed-off-by: Alex Boten <[email protected]>

CHANGELOG.md

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+# Changelog
+
+## Unreleased

RELEASING.md

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+# How to Create a Release of OpenTelemetry Configuration (for Maintainers Only)
+
+## Tagging the Release
+
+Our release branches follow the naming convention of `v<major>.<minor>.x`, while
+the tags include the patch version `v<major>.<minor>.<patch>`. For example, the
+same branch `v0.3.x` would be used to create all `v0.3` tags (e.g. `v0.3.0`,
+`v0.3.1`).
+
+In this section upstream repository refers to the main opentelemetry-configuration
+github repository.
+
+Before any push to the upstream repository you need to create a [personal access
+token](https://help.github.com/articles/creating-a-personal-access-token-for-the-command-line/).
+
+1. Create the release branch and push it to GitHub:
+
+    ```bash
+    MAJOR=0 MINOR=3 PATCH=0 # Set appropriately for new release
+    git checkout -b v$MAJOR.$MINOR.x main
+    git push upstream v$MAJOR.$MINOR.x
+    ```
+
+2. For `vMajor.Minor.x` branch:
+
+    - Create and push a tag:
+
+    ```bash
+    git checkout v$MAJOR.$MINOR.x
+    git pull upstream v$MAJOR.$MINOR.x
+    git tag -a v$MAJOR.$MINOR.$PATCH -m "Version $MAJOR.$MINOR.$PATCH"
+    git push upstream v$MAJOR.$MINOR.$PATCH
+    ```
+
+## Patch Release
+
+All patch releases should include only bug-fixes, and must avoid
+adding/modifying the public APIs. To cherry-pick one commit use the following
+instructions:
+
+- Create and push a tag:
+
+```bash
+COMMIT=1224f0a # Set the right commit hash.
+git checkout -b cherrypick v$MAJOR.$MINOR.x
+git cherry-pick -x $COMMIT
+git commit -a -m "Cherry-pick commit $COMMIT"
+```
+
+- Go through PR review and merge it to GitHub v$MAJOR.$MINOR.x branch.
+
+- Tag a new patch release when all commits are merged.
+
+## Announcement
+
+Once deployment is done, go to Github [release
+page](https://github.com/open-telemetry/opentelemetry-configuration/releases), press
+`Draft a new release` to write release notes about the new release.
+
+You can use `git log upstream/v$MAJOR.$((MINOR-1)).x..upstream/v$MAJOR.$MINOR.x --graph --first-parent`
+or the Github [compare tool](https://github.com/open-telemetry/opentelemetry-configuration/compare/)
+to view a summary of all commits since last release as a reference.
+
+In addition, you can refer to [CHANGELOG.md](CHANGELOG.md)
+for a list of major changes since last release.
+
+## Update release versions in documentations and CHANGELOG files
+
+After releasing is done, you need to update the [CHANGELOG.md](CHANGELOG.md).
+
+Create a PR to mark the new release in [CHANGELOG.md](CHANGELOG.md) on main branch.