Merge pull request faif#293 from gyermolenko/update_readme_about_tox

Update readme with notes about tox

Author: faif

README.md

@@ -117,4 +117,6 @@ When everything else is done - update corresponding part of README.
 
 
 ##### Travis CI
-Please run `flake8` and `pytest` commands locally to be sure your changes will pass CI .
+Please run `tox` or `tox -e ci37` before submitting a patch to be sure your changes will pass CI.
+
+You can also run `flake8` or `pytest` commands manually. Examples can be found in `tox.ini`.