Add documentation for useKey, i.e. (how to use symbol/special keys like = and +) #1303
Description
I'd be happy to write concise docs for this if @JohannesKlauss approves of this.
If you approve, I'll add two lines of code to the Quick Start in the README, one useKey row for the missing row in Options table in README, and maybe a paragraph or two in the docs page (haven't looked at that so not sure how much I'd write, happy to follow your input if you have an opinion).
Great lib! Very helpful so far.