docs: document CLI version resolution in CONTRIBUTING.md (#64)

## Summary

Adds a "Version resolution in Databricks CLI" section to CONTRIBUTING.md
explaining that the CLI uses `cli-compat.json` to determine which Agent
Skills version to install.

Companion PRs:
- [databricks/cli#5139](databricks/cli#5139)
- [databricks/appkit#333](databricks/appkit#333)

Signed-off-by: Pawel Kosiec <pawel.kosiec@databricks.com>

Author: pkosiec

CONTRIBUTING.md

@@ -11,6 +11,14 @@ Examples in skills and references must follow secure defaults:
 - Prefer scoped tokens over broad credentials
 - Obfuscate sensitive values: use placeholder workspace IDs (`1111111111111111`), URLs (`company-workspace.cloud.databricks.com`), and never include real tokens or passwords
 
+## Version resolution in Databricks CLI
+
+The Databricks CLI uses [`cli-compat.json`](https://github.com/databricks/cli/blob/main/internal/build/cli-compat.json)
+to determine which Agent Skills version to install for `aitools install`. The manifest maps
+CLI versions to compatible Agent Skills versions. It lives in the
+[CLI repository](https://github.com/databricks/cli) — see the
+[README](https://github.com/databricks/cli/blob/main/internal/build/README.md) for details.
+
 ## Developer Certificate of Origin
 
 To contribute to this repository, you must sign off your commits to certify