Update mailing list link in good first issue template (#8010)

Per https://groups.google.com/d/msg/pypa-dev/rUNsfIbruHM/LCEx-CB5AgAJ
the pypa-dev Google Group is now decommissioned.
Pointing to distutils-sig instead, and polishing prose.

Signed-off-by: Sumana Harihareswara <sh@changeset.nyc>

Co-authored-by: Dustin Ingram <di@users.noreply.github.com>

.github/ISSUE_TEMPLATE/~good-first-issue.md

@@ -9,6 +9,8 @@ about: For maintainers to create an issue that is good for new contributors
 <!-- End issue text, leave the following intact -->
 ---
 
-**Good First Issue**: This issue is good for first time contributors. If you've already contributed to Warehouse, work on [another issue without this label](https://github.com/pypa/warehouse/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+-label%3A%22good+first+issue%22) instead. If there is not a corresponding pull request for this issue, it is up for grabs. For directions for getting set up, see our [Getting Started Guide](https://warehouse.pypa.io/development/getting-started/). If you are working on this issue and have questions, feel free to ask them here, [`#pypa-dev` on Freenode](https://webchat.freenode.net/?channels=%23pypa-dev), or the [pypa-dev mailing list](https://groups.google.com/forum/#!forum/pypa-dev).
+**Good First Issue**: This issue is good for first time contributors. If you've already contributed to Warehouse, work on [another issue without this label](https://github.com/pypa/warehouse/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+-label%3A%22good+first+issue%22) instead. If there is not a corresponding pull request for this issue, it is up for grabs. For directions for getting set up, see our [Getting Started Guide](https://warehouse.pypa.io/development/getting-started/).
+
+If you are working on this issue and have questions, feel free to ask them here, in the [`#pypa-dev` chat channel on Freenode](https://webchat.freenode.net/?channels=%23pypa-dev), or on the [distutils-sig.python.org mailing list](https://mail.python.org/mailman3/lists/distutils-sig.python.org/).
 
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