Document adding localizations to Firefox Desktop about documentation HOT 2 CLOSED

Why https://github.com/mozilla-l10n/pm-projects/projects/1 should be documented? That's my personal way to track locales and requests, Delphine has private spreadsheets for example.

While we should remove the BitBucket reference from that doc, the process is documented in the Nightly builds section, when most of the work happens.
https://mozilla-l10n.github.io/documentation/products/firefox_desktop/adding_nightly.html

To add the locale to Firefox in Pontoon, you literally need an hg repo and the locale set up in Pontoon.

from documentation.

BitBucket reference fixed in #197. I don't think that my personal project should be documented in there, as are the many scripts that I use to track errors, or completion levels.

from documentation.