docs: Add RELEASING.md

RELEASING.md

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+# Releasing
+
+1. Run the script `release.sh` with release name in format `[library]-v[version]`:
+   ```bash
+   ./release.sh gears-compose-v1.0.0
+   ````
+
+2. The script will ask you if you want to push the release branch and create a release tag.
+
+3. Ensure `CHANGELOG.md` looks good and is ready to be published.
+   Make the necessary edits.
+
+4. Type "yes" to the console if everything is okay.
+
+5. Click the link printed in the console to create a Pull Request for release branch.
+
+6. Merge the Pull Request as soon as the "Check" workflow succeeds.
+
+Release tag push triggers a GitHub Actions workflow, which publishes the release artifacts to Maven Central and creates a GitHub release.
+
+## Manual release preparation
+
+To prepare the release manually, follow the steps the script does:
+
+1. Ensure the repository is up to date, and the main branch is checked out.
+
+2. Create the release branch with the name `release/[library]-v[version]`
+
+3. Update the version in `gradle.properties`, `build.gradle.kts` and `README.md` ("Usage" section).
+
+4. Update the `CHANGELOG.md`:
+    1. Replace `Unreleased` section with the release version
+    2. Add a link to the diff between the previous and the new version (if possible)
+    3. Add a new empty `Unreleased` section on the top
+
+5. Commit the changes, create a tag on the commit, and push it to the remote repository.
+   The tag should follow the format `[library]-v[version]`.
+
+6. Create a Pull Request for the release branch and merge it.