Add OARS and update description to be more confident

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've also tweaked the description to better describe the app as it now is, and remove redundant text as well as tweaking the tone of voice to make it more confident and encourage users to install it.