Add wagtail-factories (#23)

* Add wagtail-factories

* Update README.md

README.md

@@ -114,6 +114,7 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [Wagtail Themes](https://github.com/moorinteractive/wagtail-themes) - Site-specific theme loader for Wagtail.
 - [wagtail-schema.org](https://github.com/takeflight/wagtail-schema.org) - Schema.org JSON-LD tags for Wagtail sites.
 - [Wagtail Experiments](https://github.com/torchbox/wagtail-experiments) – A/B testing for Wagtail.
+- [Wagtail Factories](https://github.com/mvantellingen/wagtail-factories) - Factory boy classes for Wagtail.
 
 ## Tools