CG manual, pushing to staging

[Federico Bruni]

What do you think about these instructions?
http://lilypond.org/doc/v2.19/Documentation/contributor/pushing-to-staging

I have a few comments, but I'm not sure about any of them:

1. There's no real purpose in pulling and rebasing the staging branch, 
assuming that this branch should be "clean" (we should work on master 
or on a local branch).

2. That page should explain how to generate a patch with format-patch. 
I think that `git format-patch origin` works most of the times, at 
least in my setup.

3. I don't like much the `git merge` approach suggested for those who 
work with local branches, as the git log is a bit messed up (a merge 
commit is added, often faraway from the commit containing the real 
changes). I'd rather suggest using format-patch and git am even in this 
case.