Update hooks.rst

docs/plugins/hooks.rst

@@ -35,6 +35,17 @@ Executed whenever a post is retrieved, but before being sent to the client.
 
 **Allows plugins to add new navigation links to NodeBB**
 
+``filter:register.build``
+^^^^^^^^^^^^^^^^^^^^^
+
+**Argument(s)**: 
+ - `req` the express request object (javascript Object)
+ - `res` the express response object (javascript Object)
+ - `data` the data passed to the template (javascript Object)
+
+**Allows plugins to add new elements to the registration form. At the moment, the only one supported is `data.captcha`*
+
+
 ``filter:post.parse``
 ^^^^^^^^^^^^^^^^^^^^^
 
@@ -51,6 +62,11 @@ Executed when a post or signature needs to be parsed from raw text to HTML (for
 ``filter:register.check``
 ^^^^^^^^^^^^^^^^^^^^^
 
+**Argument(s)**: 
+ - `req` the express request object (javascript Object)
+ - `res` the express response object (javascript Object)
+ - `userData` the user data parsed from the form
+
 **Allows plugins to run checks on information and deny registration if necessary.**