Documentation on units and theory of dimensional analysis

[Hazelfire]

Currently, there is a lot to be desired for in terms of documentation, there are a couple of issues that are currently missing:

• No discussion of the Language server under pedant lsp
• No discussion that seconds2 means seconds squared, or seconds-1 means per second
• Confusing elements, as @NunoSempere has pointed out, like that you can't define seconds squared by 1 seconds^2, because it parses in a way you might not expect, see Some usability suggestions #5
• Not much on build instructions, especially if you're not from Linux