Fix Description= in systemd service file

[VannTen]

Description= should be a noun phrase, and not a full sentence, according to man 5 systemd.unit.

In particular, using a dot at the end result in messages like this in journalctl when running as a user service (note the superfluous dot at the end):

May 31 16:03:38 framework systemd[1180]: Started Highly customizable Wayland bar for Sway and Wlroots based compositors.. May 31 16:20:39 framework systemd[1180]: Stopping Highly customizable Wayland bar for Sway and Wlroots based compositors.... May 31 16:20:39 framework systemd[1180]: Stopped Highly customizable Wayland bar for Sway and Wlroots based compositors..