add missing bash script for releasing steps

RELEASING.md

@@ -4,6 +4,12 @@ Releasing
  1. Update the CHANGELOG.md with the version and date 
  2. Choose a tag name (e.g. `3.0.0`), this is the version number of the release.
     1. Preview releases follow the pattern `3.0.0-alpha.1`, `3.0.0-beta.1`, `3.0.0-RC.1`
+    2. Execute the script with the tag's name, the script will update the version file and create a tag.
+
+    ```bash
+    ./scripts/prepare-release.sh 3.0.0
+    ```
+
  3. Go to [GH Releases](https://github.com/PostHog/posthog-android/releases)
  4. Choose a release name (e.g. `3.0.0`), and the tag you just created, ideally the same.
  5. Write a description of the release.