Redis::CommandError (ERR value is not an integer or out of range):

If users are using Redis and getting the error message `Redis::CommandError (ERR value is not an integer or out of range):` they need to make sure to set the `:period` parameter in throttle as an integer and not a Ruby time unit (`1.second` or `1.minute`).

Added note in README to help users who choose Redis as their backing store not get stuck by this gotcha.