Add WagtailDraftail to rich text editors

https://github.com/springload/wagtaildraftail/

README.md

@@ -63,6 +63,7 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [Wagtail TinyMCE](https://github.com/isotoma/wagtailtinymce) - A TinyMCE editor integration for Wagtail.
 - [Wagtail Froala](https://github.com/jaydensmith/wagtailfroala) - Extends Wagtail to use the Froala WYSIWYG editor in RichTextField/RichTextBlock.
 - [Wagtail Medium Editor](https://github.com/dperetti/Django-wagtailmedium) - A customizable Medium Editor for Wagtail, with link anchors support.
+- [WagtailDraftail](https://github.com/springload/wagtaildraftail) – Draft.js editor for Wagtail, built upon [Draftail](https://github.com/springload/draftail) and [draftjs_exporter](https://github.com/springload/draftjs_exporter).
 
 ### Widgets