added a section about contributing to README

README.textile

@@ -508,6 +508,15 @@ Well...there's a TextMate-bundle in town, dedicated to make usage of Formtastic
 "Formtastic.tmbundle":http://github.com/grimen/formtastic_tmbundle
 
 
+h2. How to contribute
+
+*Before you send a pull request*, please ensure that you provide appropriate spec/test coverage and ensure the documentation is up-to-date.  Bonus points if you perform your changes in a clean topic branch rather than master.
+
+Please also keep your commits *atomic* so that they are more likely to apply cleanly.  That means that each commit should contain the smallest possible logical change.  Don't commit two features at once, don't update the gemspec at the same time you add a feature, don't fix a whole bunch of whitespace in a file at the same time you change a few lines, etc, etc.
+
+For significant changes, you may wish to discuss your idea on the Formtastic Google group before coding to ensure that your change is likely to be accepted.  Formtastic relies heavily on i18n, so if you're unsure of the impact this has on your changes, please discuss them with the group.
+
+
 h2. Contributors
 
 Formtastic is maintained by "Justin French":http://justinfrench.com, "José Valim":http://github.com/josevalim and "Jonas Grimfelt":http://github.com/grimen, but it wouldn't be as awesome as it is today without help from over 30 contributors.