Merge pull request #1199 from DirectXMan12/docs/common-versioning

📖 Be more specific about compat in VERSIONING

VERSIONING.md

@@ -8,3 +8,23 @@ counts as a "library project", but otherwise follows the guidelines
 exactly.
 
 [guidelines]: https://sigs.k8s.io/kubebuilder-release-tools/VERSIONING.md
+
+## Compatiblity and Release Support
+
+For release branches, we generally tend to support backporting one (1)
+major release (`release-{X-1}` or `release-0.{Y-1}`), but may go back
+further if the need arises and is very pressing (e.g. security updates).
+
+### Dependency Support
+
+Note the [guidelines on dependency versions][dep-versions].  Particularly:
+
+- We **DO** guarantee Kubernetes REST API compability -- if a given
+  version of controller-runtime stops working with what should be
+  a supported version of Kubernetes, this is almost certainly a bug.
+
+- We **DO NOT** guarantee any particular compability matrix between
+  kubernetes library dependencies (client-go, apimachinery, etc); Such
+  compability is infeasible due to the way those libraries are versioned.
+
+[dep-versions]: https://sigs.k8s.io/kubebuilder-release-tools/VERSIONING.md#kubernetes-version-compatibility