Update the release procedure (kubernetes#2565)

Seems like the point explaining how to promote images from staging is
gone, this commit adds it back, fixes formatting and moves the file into
the `docs` directory.

Author: dulek

docs/release-procedure.md

@@ -0,0 +1,44 @@
+# Release Procedure
+
+The Cloud Provider OpenStack Release is done in sync with
+kubernetes/kubernetes. Minor versions can be released intermittently for
+critical bug fixes.
+
+## Making a Release
+
+1. Checkout the release branch.
+
+    ```bash
+    $ git fetch upstream
+    $ git checkout -b my-release upstream/release-X.Y
+    ```
+
+2. Update the minor version with the expected version.
+
+    Make changes in the `docs/manifests/tests/examples` directories using the
+    `hack/bump_release.sh` script by running the following command:
+
+    ```bash
+    $ hack/bump-release.sh 28 29 0
+    ```
+
+    This will replace `1.28.x`/`2.28.x` with `1.29.0`/`2.29.0` strings in the
+    `docs/manifests/tests/examples` directories. Ensure that you double-check the
+    diff before committing the changes. Non-related changes must not be shipped.
+
+3. Create a new pull request (PR) and make sure all CI checks have passed.
+
+4. Once the PR is merged, make a tag and push it to the upstream repository.
+
+    ```bash
+    $ git checkout -b release-X.Y upstream/release-X.Y
+    $ git pull upstream release-X.Y --tags
+    $ git tag -m "Release for cloud-provider-openstack to support Kubernetes release x" vX.Y.Z
+    $ git push upstream vX.Y.Z
+    ```
+
+5. [Github Actions](https://github.com/kubernetes/cloud-provider-openstack/actions/workflows/release-cpo.yaml) will create new [Docker images](https://console.cloud.google.com/gcr/images/k8s-staging-provider-os) and generate a [new draft release](https://github.com/kubernetes/cloud-provider-openstack/releases) in the repository.
+
+6. Make PR modifying [images.yaml](https://github.com/kubernetes/k8s.io/blob/main/registry.k8s.io/images/k8s-staging-provider-os/images.yaml) to promote gcr.io images to registry.k8s.io. The point is to copy the proper image sha256 hashes from the staging repository to the images.yaml.
+
+7. Once images are promoted create release notes using the "Generate release notes" button in the GitHub "New release" UI and publish the release.