Fixed the order of args to grep in README.

I just had a tiny fix for the docs.  According to the grep man pages[0], the pattern to be searched for goes before the file it is to be searched for in.

Also, just wanted to say.  This is a very cool project, I can't wait to try it out.

[0]: http://unixhelp.ed.ac.uk/CGI/man-cgi?grep