Add instructions how to use this formula

[nerdoc]

Describe the feat you'd like
I have much experience with Python, Django, and a bit with salt. But if you don't know what a "Formula" is you have no idea how to install alcali. The alcali docs say "the easiest way of installing alcali is using the formula", pointing to this repository, but noone explains how to use a "formula". There should at least exist a link to the "formula usage" docs.

In fact, this affects some formulas.
A good example is the wireguard formula:

See the full SaltStack Formulas installation and usage instructions.

Add this line here too.