Add documentation for the scripting RPC server

[wrybyte]

Is there an existing issue for this?

• I have searched the existing issues

What feature are you suggesting?

When a game starts running, the emulator opens a UDP socket which acts as an RPC server. This server can communicate with third-party programs to aid scripting with minimal set-up.

Currently, the emulator supports two request types for reading and writing memory (and there is an open PR (#375, #601) for adding key-press and signal request types as well).

However, virtually none of this information is documented anywhere, and the only reference for how to properly interact with the RPC server is an undocumented Python client that hasn't been updated in six years.

Why would this feature be useful?

It would be great for the RPC server to be expanded even further, but there is hardly any grounds for it to be usable or maintainable.

There is a lot of potential that this feature can have for scripting, but it is hardly useful if nobody knows how to use it (or that it even exists).

I've already written some documentation that I plan to create a PR for, but I thought it was best to create an issue first.