Update README.md

It is a variation of popular pencil and paper game (aka Noughts and Crosses) inspired by problem on Google CodeJam contest. 

At first I'd like to make initial games, and then I have some ideas to make the game more interactive and funny. I want make field larger, make 'joker' cells appear at random time during the game, then make game real-time, add capital battle cruisers, space dropships, sich cossacks and nuclear carpet bombing.

The main goal for me is to learn Clojure and its libraries.