Fix typo
Merge pull request #149 from aitzol/master

Little typo in docs
Added a 'How to contribute' section.
Context manager for switching fallbacks on or off.
Merge remote-tracking branch 'upstream/master' into develop
Test and docs for the new fallbacks toggle.
Merge branch 'feature/temporarily-disable-fallbacks' into develop

Conflicts:
	modeltranslation/settings.py
	modeltranslation/tests/__init__.py