Consider moving some docs from alloc::arc to alloc::arc::Arc

[Ms2ger]

http://static.rust-lang.org/doc/master/alloc/arc/index.html has some useful docs, which are somewhat hard to find. In particular, someone on IRC misconstrued the more terse documentation on the Arc type itself to mean that it magically allowed mutable access.

CC @steveklabnik

[steveklabnik]

part of #29377

[steveklabnik]

I would be happy to work with anyone who wants to work on this issue.

[izgzhen]

@steveklabnik Can I work on this one?

@Ms2ger Do you mean the lack of more information regarding get_mut and make_mut?

[Ms2ger]

I think everything on the module page would be more discoverable on the type page; the module page could then be limited to its first line and a link to the type page.

[steveklabnik]

@izgzhen sure thing!

In general, the module page should provide an overview of the module. And each type's page should provide an in-depth view of the type.

This module is very tiny, only encompassing Arc and Weak, and so it should be relatively small.

[JustAPerson]

Looks like this can be closed?

[steveklabnik]

Yes, thanks!