Fixed #24270 -- Doc'd that django_bash_completion is only in the source distribution.

docs/ref/django-admin.txt

@@ -1770,7 +1770,7 @@ Bash completion
 ---------------
 
 If you use the Bash shell, consider installing the Django bash completion
-script, which lives in ``extras/django_bash_completion`` in the Django
+script, which lives in ``extras/django_bash_completion`` in the Django source
 distribution. It enables tab-completion of ``django-admin`` and
 ``manage.py`` commands, so you can, for instance...