Merge pull request matplotlib#25741 from meeseeksmachine/auto-backpor…

…t-of-pr-25736-on-v3.7.1-doc

Backport PR matplotlib#25736 on branch v3.7.1-doc (added assigning and duplicating section heading to contribute guide)

doc/devel/contributing.rst

@@ -89,6 +89,9 @@ though not necessarily all at the same time:
 - It involves Python features such as decorators and context managers, which
   have subtleties due to our implementation decisions.
 
+Assigning issues and duplicating pull requests
+----------------------------------------------
+
 In general, the Matplotlib project does not assign issues. Issues are
 "assigned" or "claimed" by opening a PR; there is no other assignment
 mechanism. If you have opened such a PR, please comment on the issue thread to