Doc: CG, explain other git prompt variables
The use of these environment variables is documented within the
git source code: git/contrib/completion/git-prompt.sh
Background: in January a translator using LilyDev made a
simple mistake because he did not know the meaning of the
symbols in the git prompt:
http://lilypond-translations.3384276.n2.nabble.com/More-Catalan-translations-td7572931.html
Diff:
Passes make, make check and a full make doc.
Patch on countdown for July 26th
Patch counted down - please push.
pushed to staging as commit 68dbc841e3401f14b900f6750ebb49b406caf357