add gif

docs/3.0/guides/basic-authentication.md

@@ -2,6 +2,8 @@
 
 Because in Rails we commonly do that using a static function on the controller we need to [safely extend the controller](https://avohq.io/blog/safely-extend-a-ruby-on-rails-controller) to contain that function.
 
+<img src="/assets/img/guides/basic-auth/basic-auth.gif" alt="Add Avo behind Basic Authentication" height="648" />
+
 In actuality we will end up with something that behaves like this:
 
 ```ruby{2}