Clarify that __state parameter needs to be marked as out in prefix in Patching wiki

[ManlyMarco]

Currently the wiki reads:

Patches can use a parameter named __state to store information in the prefix method that can be accessed again in the postfix method. Think of it as a local variable. It can be any type and you are responsible to initialize its value in the prefix

This can be confusing if you don't know to add out in prefix since there's no errors and in postfix you always get null.

An example with the __state parameter used would be nice too.

[DingoDjango]

I've only ever used it as ref not out

[pardeike]

I don't put more time in the current Wiki in favour and preparation of the new documentation at https://harmony.pardeike.net - it's for Harmony 2.0b only but that's how it is.