[plt-dev] Revised git intro text

Thanks - this helps considerably.

However, it's long on technical information on how one could work with
git, and short on policy, i.e. how you want us to use git for PLT.
Immediate questions:

- Should we merge or rebase?
- Should we push directly to origin/master, or somewhere else, and you
  do the pulling?  (Push doesn't scale indefinitely.)
- For longer-lived branches that we want others to see, do you want us
  to use named branches within the main repo, or user repositories?

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla