Update and rename README.textile to README.mdown

Hey @Abizern, a strange pull request - but I have corrected a small typo in the read me file and in the process formatted it as markdown. :stuck_out_tongue_winking_eye: 

The read me originally stated that you should update the submodules with `git submodule --init --recursive` . In fact the command is `git submodule update --init --recursive`.