Misc - Add Wagtail grapple (#173)

Co-authored-by: Thibaud Colas <thibaudcolas@gmail.com>

README.md

@@ -199,6 +199,7 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [Wagtail Content Import](https://github.com/torchbox/wagtail-content-import) - Import content from Google Docs or Docx into StreamFields, using a customisable mapping system.
 - [Wagtail Trash](https://github.com/Frojd/wagtail-trash) - Will place pages in a trash can from where they can be restored instead of being permanently deleted.
 - [Wagtail PDF View](https://github.com/donhauser/wagtail-pdf) - Render Wagtail pages and models as PDF document using Weasyprint or LaTeX.
+- [Wagtail Grapple](https://github.com/torchbox/wagtail-grapple) - A Wagtail app that makes building GraphQL endpoints a breeze.
 
 ## Tools