bug_report.md: ask to notify maintainers

This is really essential thing that everyone should be doing.
A few extra notifications won't hurt anyone, and we should be tracking issues
to connect them to the best people who can handle them.

Co-Authored-By: Cole Helbling <cole.e.helbling@outlook.com>

.github/ISSUE_TEMPLATE/bug_report.md

@@ -25,6 +25,12 @@ If applicable, add screenshots to help explain your problem.
 **Additional context**
 Add any other context about the problem here.
 
+**Notify maintainers**
+<!--
+Please @ people who are in the `meta.maintainers` list of the offending package or module.
+If in doubt, check `git blame` for whoever last touched something.
+-->
+
 **Metadata**
 Please run `nix-shell -p nix-info --run "nix-info -m"` and paste the result.