Doc: CG, explain other git prompt variables (issue 328890043 by address@hidden)

[fedelogy]

Reviewers: ,

Description:
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

Please review this at https://codereview.appspot.com/328890043/

Affected files (+14, -2 lines):
  M Documentation/contributor/source-code.itexi


Index: Documentation/contributor/source-code.itexi
diff --git a/Documentation/contributor/source-code.itexi  
b/Documentation/contributor/source-code.itexi
index  
ac8ecb6ee40827b3d5f137f1baeb712ab7b52870..620368280aa9bdb63e84be05462e0dda0032da18  
100644
--- a/Documentation/contributor/source-code.itexi
+++ b/Documentation/contributor/source-code.itexi
@@ -209,13 +209,25 @@ git config --global core.editor @var{nano}
 @end example

 Finally, and in some ways most importantly, let's make sure that
-we know what branch we're on.  If you're not using LilyDev, add
-this to your @file{~/.bashrc}:
+we can easily see the state of our working copy, without the need
+of typing @code{git status} repeatedly.  If you're not using
+LilyDev, add the following lines to your @file{~/.bashrc}:

 @verbatim
 export PS1="address@hidden \w\$(__git_ps1)$ "
+export GIT_PS1_SHOWDIRTYSTATE=true
+export GIT_PS1_SHOWUNTRACKEDFILES=true
+export GIT_PS1_SHOWUPSTREAM=auto
 @end verbatim

+The first line will show the branch we're on.  The other lines
+will use some symbols next to the branch name to indicate some
+kind of state. @qq{*} means that there are unstaged changes,
address@hidden indicates staged changes; if there are untracked files,
+a @qq{%} will appear.  Finally, we can also see if our HEAD is
+behind (@qq{<}) or ahead (@qq{>}) of its upstream, and if they
+have diverged (@qq{<>}) or they are synced (@qq{=}).
+
 You may need to install the additional @code{bash-completion}
 package, but it is definitely worth it.  After installation
 you must log out, and then log back in again to enable it.