Remove wagtailsurveys, link to Form Builder docs

As the repository indicates, it's now replaced by Wagtail itself.

README.md

@@ -154,7 +154,8 @@ Awesome Wagtail [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38
 
 ### Forms
 
-- [Wagtailsurveys](https://github.com/torchbox/wagtailsurveys) - A module for Wagtail which provides the ability to build polls and surveys.
+Before looking into form add-ons, take a look at [Wagtail's Form Builder](https://docs.wagtail.org/en/stable/reference/contrib/forms/).
+
 - [Wagtail ReCaptcha](https://github.com/springload/wagtail-django-recaptcha) - wagtail-django-captcha provides an easy way to integrate the [django-recaptcha](https://github.com/praekelt/django-recaptcha) field when using the Wagtail formbuilder.
 - [Wagtail Simple Captcha](https://github.com/acarasimon96/wagtail-django-simple-captcha) - A self-hosted alternative to Wagtail ReCaptcha that easily integrates a [django-simple-captcha](https://github.com/mbi/django-simple-captcha) field into the Wagtail form builder.
 - [wagtailstreamforms](https://github.com/AccentDesign/wagtailstreamforms) - Build forms in Wagtail's admin for use in streamfields.