Add release flow document

Author: kubode

RELEASING.md

@@ -0,0 +1,37 @@
+# Releasing
+
+1. Update the `version` in [`gradle.properties`](./gradle.properties) to the release version.
+
+2. Commit changes.
+
+   ```shell
+   $ git commit -am "Prepare version X.Y.X"
+   ```
+
+3. Tag the release.
+
+   ```shell
+   $ git tag -am "Version X.Y.Z" X.Y.Z
+   ```
+   
+4. Push the tag.
+
+   ```shell
+   $ git push --tags
+   ```
+
+5. Update the `version` in [`gradle.properties`](./gradle.properties) to the next `SNAPSHOT` version.
+
+6. Commit changes.
+
+   ```shell
+   $ git commit -am "Prepare next development version"
+   ```
+
+7. Push changes.
+
+   ```shell
+   $ git push && git push --tags
+   ```
+
+   This will trigger a GitHub Action to publish the library to Maven Central.