Add guide on how to hook a new function

[GeckoEidechse]

WIth R2Northstar/NorthstarLauncher#171 the way we hook functions has changed and given that we didn't even have documentation for the old method, now would be a good time to change it.

Basically a guide on how to hook a function would be a good way to introduce someone to the topic and teach them how to do it themselves.

The place to put it would be somewhere in the Reverse Engineering section: https://r2northstar.readthedocs.io/en/latest/reverse-engineering/introduction.html