Fixed typo in README.md.

Fixed typo.

To paraphrase the great Austin Powers, "this is me in a nuthsell".

Oh wait, he probably said "nutshell".

Yes, yes he did:

> [Vanessa Kensington](http://www.imdb.com/name/nm0000167/?ref_=tt_trv_qu): Always wanting to have fun, Austin. That's you in a nutshell!
>
> [Austin Powers](http://www.imdb.com/name/nm0000196/?ref_=tt_trv_qu): No, this is me in a nutshell.
> [acts as if he were in a nutshell]
>
> [Austin Powers](http://www.imdb.com/name/nm0000196/?ref_=tt_trv_qu): Help! I'm in a nutshell! How did I get into this nutshell? Look at the size of this bloody great big nutshell! What sort of shell has a nut like this? This is crazy!