[Gallery] Update README with steps to create a release (#327)

gallery/README.md

@@ -72,3 +72,31 @@ more details):
 ```
 flutter pub run grinder update-code-segments
 ```
+
+## Creating a new release (for Flutter org members)
+
+1. Bump the version number up in the `pubspec.yaml`. Use semantic versioning to determine 
+   which number to increment. For example `2.2.0+020200` should become `2.3.0+020300`.
+   
+2. Create a tag on the `master` branch of this repo in the form of `gallery-v2.3`.
+	* `git tag gallery-v2.3`
+	* `git push --tags`
+
+3. Publish the web release (using the [peanut package](https://pub.dev/packages/peanut)).
+    * `flutter pub global activate peanut`
+    * `flutter pub global run peanut:peanut`
+    * `git push upstream gh-pages:gh-pages`
+        * `git update-ref refs/heads/gh-pages upstream/gh-pages` if you need to align with upstream.
+
+4. Publish the Android release (using the correct signing certificates).
+    * Create the app bundle with `flutter build appbundle`.
+    * Upload to the Play store console.
+    * Publish the Play store release.
+    * Create the APK with `flutter build apk` (this is for the Github release).
+
+5. Draft a release in Github from the tag you created, call the release `Flutter Gallery 2.3`
+    * Upload the Android APK from above.
+    * Create and upload the macOS build by running `flutter build macos` and zipping the 
+      app inside `build/macos/Build/Products/Release`.
+    * Optional: Create and upload the Linux/Windows builds.
+    * Publish the release.