Mark the toolbar as unmaintained.

Author: aaugustin

README.rst

@@ -33,4 +33,7 @@ itself. If you like it, please consider contributing!
 The Django Debug Toolbar was originally created by Rob Hudson <[email protected]>
 in August 2008 and was further developed by many contributors_.
 
+**There's no active maintainer at this time. You're welcome to file issues and
+pull requests but you may receive no answer until a new maintainer steps up.**
+
 .. _contributors: https://github.com/django-debug-toolbar/django-debug-toolbar/graphs/contributors