updated contributing with tox info

docs/contributing.rst

@@ -1,37 +1,38 b''
 .. _contributing:
 
 =========================
 Contributing to RhodeCode
 =========================
 
 If you would like to contribute to RhodeCode, please contact me, any help is
 greatly appreciated!
 
 Could I request that you make your source contributions by first forking the
 RhodeCode repository on bitbucket_
 https://bitbucket.org/marcinkuzminski/rhodecode and then make your changes to
 your forked repository. Please post all fixes into **BETA** branch since your 
 fix might be already fixed there and i try to merge all fixes from beta into
 stable, and not the other way. Finally, when you are finished making a change, 
 please send me a pull request.
 
 To run RhodeCode in a development version you always need to install the latest
 required libs from `requires.txt` file.
 
 after downloading/pulling RhodeCode make sure you run::
 
     python setup.py develop
 
 command to install/verify all required packages, and prepare development 
 enviroment.
 
 
 After finishing your changes make sure all tests passes ok. You can run
-the testsuite running ``nosetest`` from the project root.
+the testsuite running ``nosetest`` from the project root, or if you use tox
+run tox for python2.5-2.7 with multiple database test.
 
 | Thank you for any contributions!
 |  Marcin
 
 
 
 .. _bitbucket: http://bitbucket.org/