docs on contract_library_method noir annotation

[critesjosh]

prevents the method from being a "function" that another contract can call. It becomes a helper method for a contract and should not be seen as the entry point.

(comes from this PR)

it esentially marks a method as a non entry point in a contract scope, it basically means that it will not show up on the contract abi, and its only purpose is to be a helper method

its not a macro, but rather an annotation to say do not compile this as an entrypoint for methods defined in the contract scope