Improve user experience

[jeremyd2019]

Right now, this is a thin wrapper around msys2-autobuild workflows, the inputs are exactly the same as the workflow inputs, and their labels are copy/pasted from the workflow yml. This is not user-friendly, and it's not obvious how the inputs are supposed to be used. As a proper website, this can do better here.

[jeremyd2019]

Related #1 which was my first idea to improve user experience, but inputs other than cycles could use improvement too.