Documentation: Describe supported scoring systems (with visual examples?)

[TomHall2020]

It would be helpful to have a section in the docs with a bit of a blurb on each of the supported scoring systems to help users figure out which one they want to use. Some graphical representations of the targets would be even better.

Not going to sign up to implement this one as I'd like to get #56 squared off and then I need to focus back on archr for a while, but its probably not urgent.

[jatkinson1000]

Yep, this is something I can look at on a rainy day.

I'll try and get #2 done soon now that I think I have settled on an approach which should help you for archr, and also the last major hurdle for #49 (just #15 I think).