State minimal length of key

[Andreyco]

You should state that minimal key length is 62 characters (or you won't be able to properly decode IDs for integers of higher value). Is it minimal length or should be exact length? Whatever, please state this requirement in readme.

Thank you for your work

[lschricke]

Hello! First, thanks for this nice piece of software! Very useful! :) I agree with Andreyco, either a statement in the readme, or maybe checking the validity of the key when creating the Tiny object to ensure proper encoding/decoding. What do you think? Thanks!