Add docs page for how a typical REST API request works

[rmccue]

Last year at WCEU, @kadamwhite took notes on how a typical REST API request works in WordPress from the top down. We need to get this into some actual form on the handbook.

[jonathanbossenger]

@kadamwhite I know it's almost 5 years later, but do you still perhaps have these notes? If so, I'd be happy to turn them into a page in the handbook.