chore: update contributing.md to explicitely outline dep updates

Author: darcyclarke

CONTRIBUTING.md

@@ -51,6 +51,10 @@ We've set up an automated [benchmark](https://github.com/npm/benchmarks) integra
 
 You can learn more about this tool, including how to run & configure it manually, [here](https://github.com/npm/benchmarks)
 
+## Dependency Updates
+
+It should be noted that our team does not accept third-party dependency updates/PRs. We have a [release process](https://github.com/npm/cli/wiki/Release-Process) that includes checks to ensure dependencies are staying up-to-date & will ship security patches for CVEs as they occur. If you submit a PR trying to update our dependencies we will close it with or without a reference to these contribution guidelines.
+
 ## Reporting Bugs
 
 When submitting a new bug report, please first [search](https://github.com/npm/cli/issues) for an existing or similar report & then use one of our existing [issue templates](https://github.com/npm/cli/issues/new/choose) if you believe you've come across a unique problem. Duplicate issues, or issues that don't use one of our templates may get closed without a response.