If you want to contribute you should create your own github account, and clone the FitNesse project. Then you can make your changes and finally send a pull request to the FitNesse project owner. There is a button on the github site that does that.

If you have a patch that you would like to submit, or if you would like to become a regular submitter to FitNesse, then contact unclebob@cleancoder.com">Uncle Bob Martin.

It's also a good idea to post your patches to the fitnesse yahoo group. http://tech.groups.yahoo.com/group/fitnesse