update the supervisor script and conf

now, we auto add the start.sh -> /usr/bin/gogs_start, then supervisor
needn’t the full path, detail please see the commit.
and how to use:
entry gogs root path, then input
scripts/gogs_supervisord.sh restart (add sudo if need)
add auto start script

how to use:
vim /etc/rc.local, then add
cd /home/git/gogs; scripts/autoboot.sh
(goes path you can replace your path)
Merge pull request #556 from jacksonpan/master

update the supervisor script and conf