chore: add documentation for releasing this extension

Signed-off-by: Florent BENOIT <fbenoit@redhat.com>

RELEASE.md

@@ -0,0 +1,10 @@
+# Release
+
+To create a release, go to GitHub actions and run a custom workflow release:
+https://github.com/containers/podman-desktop-extension-minikube/actions/workflows/release.yaml
+
+To cut a 0.2.0 release with a v0.2.0 tag, start a new job clicking `Run workflow ⬇️` button.
+Enter '0.2.0' in the form and click on 'Run workflow' green button.
+
+It will do the job and create a Pull Request to upgrade to `0.3.0-next`.
+Please approve it and it will automatically merge the pull request when PR checks are done.