This is used by Software Centers and packaging systems that make use of
the AppStream specification. It adds distribution independent metadata
for the project.

Screenshots are not supplied due to the extra work needed to make new
ones that comply with the AppStream recommendations. Specifically the
difficulty lies in only showing the window, yet maintaining an aspect
ratio of 16:9.

Not sure how this is best solved. Likely the only solution is to
something similar to the current screenshot.jpg, minus the background
and no padding.

This appdata file validates using `appstream-util validate-relax`.

Should fix #121

Go For It! is now available on flathub. Basic instructions on how to get
started helps users find this.

Instructing users to use `yaourt` is wrong. Mostly because aur helpers
are unsupported by the Arch Linux developers. But also because `yaourt`
is no longer a good choice.

Instead presenting a user with the archlinux wiki page, with relevant
information is a good practice.

There is also a stable AUR package now, so linking to that is more
sensible. Keeping both though, just in case.

Add flatpak instructions and change archlinux instructions.

Add appdata file