Add wagtail-metadata-mixin app (#12)

README.md

@@ -104,6 +104,7 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [wagtailmenus](https://github.com/rkhleics/wagtailmenus) - An extension for Torchbox's Wagtail CMS to help you manage and render multi-level navigation and simple flat menus in a consistent, flexible way.
 - [Wagtail Error Pages](https://github.com/alexgleason/wagtailerrorpages) - Pretty, smart, customizable error pages for Wagtail.
 - [wagtail-metadata](https://github.com/takeflight/wagtail-metadata) - A tool to assist with metadata for social media and search engines.
+- [wagtail-metadata-mixin](https://github.com/bashu/wagtail-metadata-mixin) - OpenGraph, Twitter Card and Google+ snippet tags for Wagtail CMS pages.
 - [Wagtail Analytics](https://github.com/tomdyson/wagalytics) - A Google Analytics dashboard in your Wagtail admin.
 - [Django Wagtail Feeds](https://github.com/chrisdev/django-wagtail-feeds) - Add support for RSS Feeds, Facebook Instant Articles and Apple News Publisher to your Wagtail CMS Projects.
 - [Wagtail Themes](https://github.com/moorinteractive/wagtail-themes) - Site-specific theme loader for Wagtail.