Add OARS tags, make description more inviting

OARS is a standard that allows Software Stores (such as GNOME Software) to apply local ratings to applications. It's a requirement for new apps on Flathub and it'd be great to get it upstream into existing apps as well.

I also rewrote the description to be a bit more inviting and describe the features. Hopefully it means more people will install it from GNOME Software.