Initial shared Copilot resources scaffold

docs/versioning.md

@@ -0,0 +1,10 @@
+# Versioning
+
+This repository versions the shared resource set as a whole through Git.
+
+## Compatibility
+
+- Additive resources are preferred and should not require coordinated rollout.
+- Renames and removals should be treated as breaking changes.
+- If a resource changes behavior in a non-obvious way, document it in the
+  change description and deprecation notes.