I'm actually hoping this is an embarrassing question but how do you get 
the tail end of a string?  All I've figured out is this:

index = 4
string[index, string.size - index]

    ...but surely there's a better way.  This happens to me a lot and I 
really appreciate Python's curt syntax in this case:  string[index:]
    What's the Ruby way?
    Thank you!