add release instruction

Author: dinhtungdu

CONTRIBUTING.md

@@ -28,6 +28,14 @@ This repository currently uses the `develop` branch to reflect active work and `
 
 ## Release instructions
 
-1. [Create a new release](https://github.com/10up/action-wordpress-plugin-deploy/releases/new)
-2. Ensure it appears in the GitHub Marketplace correctly
-3. Celebrate shipping!
+1. Branch: Starting from `develop`, cut a release branch named `release/X.Y.Z` for your changes.
+1. Changelog: Add/update the changelog in `CHANGELOG.md`.
+1. Props: update `CREDITS.md` file with any new contributors, confirm maintainers are accurate.
+1. Readme updates: Make any other readme changes as necessary in `README.md`.
+1. Merge: Make a non-fast-forward merge from your release branch to `develop` (or merge the pull request), then do the same for `develop` into `stable` (`git checkout stable && git merge --no-ff develop`).
+1. Push: Push your trunk branch to GitHub (e.g. `git push origin stable`).
+1. Release: Create a [new release](https://github.com/10up/action-wordpress-plugin-deploy/releases/new), naming the tag and the release with the new version number, and targeting the `stable` branch. Paste the changelog from `CHANGELOG.md` into the body of the release and include a link to the closed issues on the [milestone](https://github.com/10up/action-wordpress-plugin-deploy/milestones/#?closed=1).  The release should now appear under [releases](https://github.com/10up/action-wordpress-plugin-deploy/releases).
+1. Ensure it appears in the GitHub Marketplace correctly.
+1. Close milestone: Edit the [milestone](https://github.com/10up/action-wordpress-plugin-deploy/milestones/) with release date (in the `Due date (optional)` field) and link to GitHub release (in the `Description field`), then close the milestone.
+1. Punt incomplete items: If any open issues or PRs which were milestoned for `X.Y.Z` do not make it into the release, update their milestone to `X.Y.Z+1`, `X.Y+1.0`, `X+1.0.0` or `Future Release`.
+1. Celebrate shipping!