document how to make non-utf8 byte vectors with bytes!(…)

[iampiyush]

This behaviour should be explained in documentation.

use of bytes!("hell", 0xc0, 0xca, "o!") instead of bytes!("hell\xc0\xca\o1!")

[catamorphism]

(bug triage) No updates.

[Valloric]

I just encountered the same issue of needing exactly what bytes! provides, but couldn't find it in the docs since it wasn't there.