Merge pull request #21068 from Homebrew/contributing_discussions

CONTRIBUTING: note Homebrew/discussions.

Author: MikeMcQuaid

CONTRIBUTING.md

@@ -13,4 +13,8 @@ First time contributing to Homebrew? Read our [Code of Conduct](https://github.c
 
 * Open an issue with a detailed description of your proposed feature, the motivation for it and alternatives considered. Please note we may close this issue or ask you to create a pull-request if this is not something we see as sufficiently high priority.
 
+### Discuss, ask questions about or disagree with changes in Homebrew
+
+* [Homebrew/discussions](https://github.com/orgs/Homebrew/discussions) is the place for community discussions around Homebrew. We aim to keep our issues and pull requests focused on discussing work to be done, not asking questions about usage or disagreeing with changes already made.
+
 Thanks!