There's no standard policy or procedure for granting commit access to the repository.  Usually it goes like "someone asks for it, someone gives it to them".

I got them. 

Is there a wiki page describing how buildbot should be used?

I found some notes hidden in the review process page... it looks like builds are triggered from the web page with click.

The review page also talks about a misterious force-builds.py script which is not part of the main twisted repo.. or at least, I could not found it

I was expecting a buidbot try scheduler  and use buildbot command line tools to trigger remote tests