Add release process documentation

Author: mboersma

docs/releasing.md

@@ -0,0 +1,68 @@
+# How to Create a CAAPH Release
+
+This document describes the process for creating a new release of the Cluster API Addon Provider Helm (CAAPH). This process requires maintainer access to the repository.
+
+1. **Check out code at the correct commit.**
+
+    Currently this project releases from the `main` branch. Make sure your local copy of the code is up to date:
+
+    ```shell
+    git checkout main
+    git fetch upstream
+    git rebase upstream/main
+    ```
+
+2. **Choose the next semantic version.**
+
+    Choose the next patch or minor version by incrementing the latest tag:
+
+    ```shell
+    git describe --tags --abbrev=0
+    export RELEASE_VERSION=v0.2.1  # Replace "v0.2.1" with the actual next version
+    ```
+
+3. **Tag the code and push it upstream.**
+
+    ```shell
+    git push upstream main
+    git tag -a $RELEASE_VERSION -m $RELEASE_VERSION
+    git push upstream $RELEASE_VERSION
+    ```
+
+4. **Wait for a tagged image in the staging repository.**
+
+    Pushing the new tag will trigger a [testgrid job](https://testgrid.k8s.io/sig-cluster-lifecycle-image-pushes#post-cluster-api-addon-provider-helm-push-images) to build and push a CAAPH image to the [staging repository](https://console.cloud.google.com/gcr/images/k8s-staging-cluster-api-helm?project=k8s-staging-cluster-api-helm). Wait for the job to complete and for the tagged image to be available before proceeding.
+
+5. **Promote the release image.**
+
+    Run the `make promote-images` command to promote the image from the staging repository to the production repository. If your git remotes don't use `https://` URLs, set the `USER_FORK` environment variable to your GitHub username.
+
+    ```shell
+    USER_FORK=<username> make promote-images
+    ```
+
+    This command will create a Pull Request at [k8s.io](https://github.com/kubernetes/k8s.io/pulls) to promote the image to production. Double-check that the SHA added by the PR matches the SHA of the staging image.
+    
+    See an [example PR](https://github.com/kubernetes/k8s.io/pull/6652).
+
+6. **Wait for the release image to be available.**
+
+    After the PR to promote the image has been approved and merged, wait for the CAAPH image to be available:
+    
+    ```shell
+    docker pull registry.k8s.io/cluster-api-helm/cluster-api-helm-controller:${RELEASE_VERSION}
+    ```
+
+7. **Update and publish the release on GitHub.**
+
+    Pushing the new tag also triggered a [GitHub Action](https://github.com/kubernetes-sigs/cluster-api-addon-provider-helm/actions/workflows/release.yml) which creates [a draft release](https://github.com/kubernetes-sigs/cluster-api-addon-provider-helm/releases).
+
+    Edit the draft release and click the "Generate release notes" button. This will populate the release notes with the PRs merged since the last release. 
+
+    If they contain any merge commits authored by a bot, click through to the original PR, then update the reference so that the actual author is credited.
+
+    Once you are satisfied with your changes, publish the release so it's no longer a draft.
+
+8. **Publicize the release.**
+
+    Announce the new release on the [CAPI Slack channel](https://kubernetes.slack.com/archives/C8TSNPY4T).