Add Wagtail Transfer (#159)

Co-authored-by: Loic Teixeira <hello@lta.me>

README.md

@@ -184,6 +184,7 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 - [Wagtail Condensed Inline Panel](https://github.com/wagtail/wagtail-condensedinlinepanel) - Drop-in replacement for Wagtail's InlinePanel suited for large number of inlines (collapsible with drag and drop support).
 - [Joyous](https://github.com/linuxsoftware/ls.joyous) - A calendar application for Wagtail.
 - [Wagtail App Pages](https://github.com/mwesterhof/wagtail_app_pages) - Extend Wagtail pages using an actual URL config and django views.
+- [Wagtail Transfer](https://github.com/wagtail/wagtail-transfer) - An official extension for Wagtail allowing content to be transferred between multiple instances of a Wagtail project
 - [Wagtail Import Export](https://github.com/torchbox/wagtail-import-export) - Import/Export pages between Wagtail instances.
 - [Wagtail Import/Export Tool](https://github.com/berkalpyakici/wagtail-import-export-tool) - Refactor of [Wagtail Import Export](https://github.com/torchbox/wagtail-import-export). This tool supports importing/exporting images, documents, and snippets that are used on imported/exported pages.
 - [Wagtail Tag Manager](https://github.com/jberghoef/wagtail-tag-manager) - A Wagtail addon that allows for easier and GDPR compliant administration of scripts and tags.