update README.md "Contributing to Newclass"

Fork it, please follow [Fork A Repo](https://help.github.com/articles/fork-a-repo)

	git remote add upstream git@github.com:twers/re-education.git

Fetch and merge the upstream
	
	git fetch upstream
	git merge upstream/master

Send the pull request, please follow [Using Pull Requests](https://help.github.com/articles/using-pull-requests)