Guide: Standard input

I had a big call for a bikeshed, and we all ended up with https://github.com/steveklabnik/guessing_game/blob/master/src/guessing_game.rs , which is what I'm building to. 

I kinda agree with you, but not being able to read a line from stdin is a pretty exceptional case in this situation, and the entire program is useless in that case, therefore, `fail`ing makes sense.