document metric-gen tag creation

Author: chrischdi

RELEASE.md

@@ -30,7 +30,8 @@ Maintaining the release branches for older minor releases happens on a best effo
     * All lines should be full sentences
   * kube-state-metrics image tag used in Kubernetes deployment yaml config.
 * Cut the new release branch, e.g. `release-1.2`, or merge/cherry-pick changes onto the minor release branch you intend to tag the release on
-* Cut the new release tag, e.g. `v1.2.0-rc.0`
+* Cut the new release tag, e.g. `v1.2.0-rc.0`.
+* Also cut the tag for metric-gen, e.g. `exp/metric-gen/v1.2.0-rc.0`.
 * Create a new **pre-release** on github
 * New images are automatically built and pushed to `gcr.io/k8s-staging-kube-state-metrics/kube-state-metrics`
 * Promote image by sending a PR to [kubernetes/k8s.io](https://github.com/kubernetes/k8s.io) repository. Follow the [example PR](https://github.com/kubernetes/k8s.io/pull/3798). Use [kpromo pr](https://github.com/kubernetes-sigs/promo-tools/blob/main/docs/promotion-pull-requests.md) to update the manifest files in this repository, e.g. `kpromo pr --fork=$YOURNAME -i --project=kube-state-metrics -t=v2.5.0`