Partly inspired by GNU coreutils HACKING[*].
doc/coding section "git" is now redundant, except for the note on
avoiding whitespace changes. Move that to section "Code formatting",
and delete section "git".
[*] http://git.savannah.gnu.org/cgit/coreutils.git/plain/HACKING?id=77da73c
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
