rbxmk documentation

With this commit, built-in rbxmk documentation is finally readable again. Formatting text is frustrating. There’s lots of comments because I barely know how it works.

https://github.com/Anaminus/rbxmk/commit/857c0dac32b1dbace20ddcb370563f2d0824b16a

I could do a release, but I’m kind of waiting for Go 1.18 to drop.