docs: update contributing label section (#8778)

docs/CONTRIBUTING.md

@@ -20,8 +20,8 @@ We're always looking for contributors.
 
 * Documentation - something missing or unclear? Please submit a pull request!
 * Code contribution - investigate
-  a [help wanted issue](https://github.com/argoproj/argo-workflows/issues?q=is%3Aopen+is%3Aissue+label%3A%22help+wanted%22+label%3A%22good+first+issue%22)
-  , or anything labeled with "good first issue"?
+  a [good first issue](https://github.com/argoproj/argo-workflows/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22)
+  , or anything not assigned.
 * Join the `#argo-contributors` channel on [our Slack](https://argoproj.github.io/community/join-slack).
 * Get a [mentor](mentoring.md) to help you get started.