Mention all match arms must return same type

[jpmelos]

I would like to propose that we should mention that all arms of a match expression should return the same type. I believe it should be noted in the section that mentions that match is an expression, and its return value can be bound to variables. The fact that its arms must return the same type is not immediately obvious, but it is possible to argue that it is a very important fact.

I don't know why, but most (all?) internal links have a <!-- ignore --> annotation, so I added one here too... Let me know if I should remove it.

[chriskrycho]

Thanks, I see what you’re going for here. I am going to go ahead and close this one, though, because I think users should be able to figure it out without having it spelled out for them! One thing to note is that we are trying to find ways not to increase the already-long text. Here, the fact that a match returns a value should connect well to the things people already know (including about if expressions and types and values in Rust in general!), so this should be fairly self-evident. If not, the compiler will help!