docs: Document SpinLock and RWLock

[Zildj1an]

Document locking support. This is related to issue #74 Document COCONUT-SVSM.

[00xc]

Looks good, just a few notes:

• When mentioning a type (e.g. RWLock, WriteLockGuard) I'd add a link to the type with square brackets.
• I'd avoid documenting trait implementations unless something counterintuitive is going on, as the docs for the trait itself should suffice. The generated docs already include links to the Rust core library documentation.
• This is just a preference, but I'd hide imports in doctests with # to clean the generated docs.

[joergroedel]

Looks good, just a few notes:

• When mentioning a type (e.g. RWLock, WriteLockGuard) I'd add a link to the type with square brackets.
• I'd avoid documenting trait implementations unless something counterintuitive is going on, as the docs for the trait itself should suffice. The generated docs already include links to the Rust core library documentation.
• This is just a preference, but I'd hide imports in doctests with # to clean the generated docs.

Given these discussions it would be helpful if you two can come up with a documentation style document. For the virtual memory code the doc domments look quite different and some common guidelines will help to better align the style.

[Zildj1an]

I have applied your feedback @00xc -- except for hiding imports, because I personally prefer seeing them; we can discuss this while preparing guidelines as @joergroedel suggested.

[Zildj1an]

Thanks @00xc I applied the feedback