Add changelog entry for wagtailforms

CHANGELOG.txt

@@ -7,6 +7,7 @@ Changelog
  * Support for alternative image processing backends such as Wand, via the WAGTAILIMAGES_BACKENDS setting
  * Added support for generating static sites using django-medusa
  * Added custom Query set for Pages with some handy methods for querying pages
+ * Added 'wagtailforms' module for creating form pages on a site, and handling form submissions
  * Editor's guide documentation
  * Editor interface now outputs form media CSS / JS, to support custom widgets with assets
  * Migrations and user management now correctly handle custom AUTH_USER_MODEL settings