Brandon Philips 9053b11b66 fix(systemd): provide a better description
Fix-up the docker service file description to declare what the service is not what it does.

When a systemd machine starts up the Description of each unit scrolls by instead of the service's filename. Because the current description doesn't say what it is it isn't very friendly:

```
Oct 31 20:40:49 localhost systemd[1]: Started Update Engine.
Oct 31 20:40:49 localhost systemd[1]: Starting Multi-User System.
Oct 31 20:40:49 localhost systemd[1]: Reached target Multi-User System.
Oct 31 20:40:49 localhost systemd[1]: Starting Easily create lightweight, portable, self-sufficient containers from any application!...
Oct 31 20:40:49 localhost systemd[1]: Started Easily create lightweight, portable, self-sufficient containers from any application!.
```
Upstream-commit: 393562340c6f386a837eac9a616c456dc54faa4f
Component: engine
2013-10-31 14:41:49 -07:00
Description
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