docs: document release process

RELEASE.md

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+# Release Process
+
+## New Patch Release (vX.Y.Z)
+
+In order to cut a new patch release from an existing release branch `release-X.Y`, follow these steps:
+
+- Run the [Tag workflow][tag-workflow] on the `release-X.Y`branch with the proper release version, `vX.Y.Z`. Message suggested, but not required: `Release vX.Y.Z`.
+- Draft the [new release notes], and share them with the rest of the team to ensure that all the required information is included.
+- Publish the above release notes.
+
+## New Minor Release (vX.Y.0)
+
+In order to cut a new minor release, follow these steps:
+
+- Create a new release branch `release-X.Y` from `master`, using the [GitHub UI][create-branch].
+- Run the [Tag workflow][tag-workflow] on the `release-X.Y`branch with the proper release version, `vX.Y.0`. Message suggested, but not required: `Release vX.Y.0`.
+- Draft the [new release notes], and share them with the rest of the team to ensure that all the required information is included.
+- Publish the above release notes.
+
+
+<!-- Named Links -->
+[create-branch]: https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/creating-and-deleting-branches-within-your-repository
+[new release notes]: https://github.com/crossplane/crossplane-runtime/releases/new
+[tag-workflow]: https://github.com/crossplane/crossplane-runtime/actions/workflows/tag.yml