Assumption that the user does not modify vanilla Emacs

[witek]

I have just spent a lot of time chasing the cause for very weird behavior. Then I found this in the source code:

;; NOTE: meow assumes that the user does not modify vanilla Emacs keybindings, otherwise extra complexity will be introduced.

I suggest to put this very prominently on the README and as a comment in the (meow-setup) function examples.