Send kind in reference manual

[jesse99]

The section on type kinds talks about sendable type kinds, but does not mention the name of the sendable kind.

[graydon]

The name is send. Section 8.5:

Rust has three kinds: 'noncopyable', 'copyable', and 'sendable'. By
default, type parameters are considered to be noncopyable. You can
annotate them with the `copy` keyword to declare them copyable, and
with the `send` keyword to make them sendable.

Closing this, I think it's covered. Reopen if you disagree?

[jesse99]

I don't have permission to re-open, but you're citing the tutorial not the reference manual. If I want to figure out syntax I should be able to use the reference manual and not some non-normative reference.