Add WagtailGridder to the list. (#33)

* Add WagtailGridder to the list.

* Move project to another section and remove demo

README.md

@@ -137,6 +137,7 @@ 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 Sharing](https://github.com/cfpb/wagtail-sharing) – Easier sharing of Wagtail drafts.
 - [Wagtail Postgres Search Backend](https://github.com/leukeleu/wagtail-pg-search-backend) - PostgreSQL full text search backend for Wagtail CMS.
+- [Wagtail Gridder](https://github.com/wharton/wagtailgridder) - Grid card layout similar to Google image search results, with an expanded area for card details.
 
 ## Tools