Mention the existence of Django admin in docs

[Endeer]

Hello,

I've set up Pontoon for small community translation of a game, and since I had no beforehand experience with Django (and basically only a little experience with Python), it took me quite a while to realize Django has generic admin page located at /a/ which is not mentioned anywhere.

Now I can create terminology items without running mange.py shell and digging into the code...

Just one line in docs would be sufficient, the "Localizing your projects" part is not very long. Should I try a pull request, or will someone be so kind? Maybe second line that this is where you should set up terminology items, and not in the Terminology project via Manage Strings.

Thanks.

[mathjazz]

Our docs are indeed in a pretty poor state, hence the https://github.com/mozilla/pontoon/pull/1570. One of the problems is that it's spread across various places. The PM docs are pretty well hidden.

A PR would be very welcome!