Return from loop is not metioned as well as loop labels

[Yanpas]

It seems that return form loop is not mentioned.

let a = loop {
	break 1;
};

There is no metion for loop labels too

[carols10cents]

Returning from a loop is covered in the newest features appendix; it was added to Rust after we froze chapter 3 for print.

The newest features appendix will be incorporated into chapter 3 in a future version. Thanks!