systemd config file uses full path to git binary.

Fixes #923

Author: reitzig

book/04-git-server/sections/git-daemon.asc

@@ -30,7 +30,7 @@ Simply place a file in `/etc/systemd/system/git-daemon.service` with these conte
 Description=Start Git Daemon
 
 [Service]
-ExecStart=git daemon --reuseaddr --base-path=/srv/git/ /srv/git/
+ExecStart=/usr/bin/git daemon --reuseaddr --base-path=/srv/git/ /srv/git/
 
 Restart=always
 RestartSec=500ms
@@ -50,6 +50,8 @@ You might have noticed that Git daemon is started here with `git` as both group
 
 Modify it to fit your needs and make sure provided user exists on the system.
 
+Also, make sure that the Git binary is indeed located at `/usr/bin/git` and change the path if necessary.
+
 Finally, you'll run `systemctl enable git-daemon` to automatically start the service on boot, and can start and stop the service with, respectively, `systemctl start git-daemon` and `systemctl stop git-daemon`.
 
 Until LTS 14.04, Ubuntu used upstart service unit configuration.