add: MDXEditor inclusion (#222)

README.md

@@ -78,6 +78,7 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [Wagtail EditorJS](https://github.com/Nigel2392/wagtail_editorjs) - An [EditorJS](https://editorjs.io/) widget with great support for Wagtail's page, image and document choosers.
 - [Wagtail Terms](https://github.com/smark-1/wagtailterms) - A plugin to add a glossary terms entity to the Draftail editor.
 - [Wagtail Text Alignment](https://github.com/Nigel2392/wagtail_text_alignment) - Align text, headings and more in your Wagtail richtext editor.
+- [wagtailmdx](https://github.com/TheBestDestroyer/wagtailmdx) - A [MDXEditor](https://github.com/mdx-editor/editor) integration for Wagtail as textfield widget.
 
 ### Widgets