ReleaseEngineering/How Tos/Enable nightly updates for a project branch

1. Pick a channel name. Unless you have a reason for it to be different, this should be "nightly-$projectbranch", eg: nightly-elm.
2. If this channel will eventually merge back to the main "nightly" channel, you *must* ensure it uses the correct MAR signing settings from the start. To do that, add the channel name to this list in the project branch repository.
3. Enable nightly builds in CI (Buildbot/Taskcluster). Make sure they are set-up to use the nightly signing servers if this channel will eventually merge back to the main "nightly" channel! Some inspiration for Buildbot can be found in project_branches.py.
4. After the first set of nightlies has successfully completed, you can enable updates in Balrog by creating a new Rule with the following data:
   • Product: Firefox
   • Channel: (the channel name you chose)
   • Mapping: Firefox-$projectbranch-nightly-latest
   • Rate: 100
   • Priority: 90

That's it! Once the next set of nightlies has successfully built, anyone running one of the original nightly builds should get updated.