Document the process for adding a new platform to the Firefox release pipeline

The process for adding builds for a new computing platform is only documented in Bugzilla (as far as I know.)

It would be useful to have a How-To guide that outlines the common requirements, like l10n changesets and bouncer entries, for example.

Since past bugs can be used as references to piece together the process, having a document seems feasible and would make it easier to repeat.