rename CAPTCHA_SETUP

this is rst so name it accordingly

README.rst

@@ -180,8 +180,8 @@ old key cached. If you update the signing key, you should change the name of the
 key in the <server name>.signing.key file (the second word) to something different.
 
 By default, registration of new users is disabled. You can either enable
-registration in the config by specifying ``enable_registration: true``
-(it is then recommended to also set up CAPTCHA - see docs/CAPTCHA_SETUP), or
+registration in the config by specifying ``enable_registration: true`` (it is
+then recommended to also set up CAPTCHA - see `<docs/CAPTCHA_SETUP.rst>`_), or
 you can use the command line to register new users::
 
     $ source ~/.synapse/bin/activate

docs/CAPTCHA_SETUP → docs/CAPTCHA_SETUP.rst

@@ -10,13 +10,13 @@ https://developers.google.com/recaptcha/
 
 Setting ReCaptcha Keys
 ----------------------
-The keys are a config option on the home server config. If they are not 
-visible, you can generate them via --generate-config. Set the following value:
+The keys are a config option on the home server config. If they are not
+visible, you can generate them via --generate-config. Set the following value::
 
   recaptcha_public_key: YOUR_PUBLIC_KEY
   recaptcha_private_key: YOUR_PRIVATE_KEY
-  
-In addition, you MUST enable captchas via:
+
+In addition, you MUST enable captchas via::
 
   enable_registration_captcha: true
 
@@ -25,7 +25,6 @@ Configuring IP used for auth
 The ReCaptcha API requires that the IP address of the user who solved the
 captcha is sent. If the client is connecting through a proxy or load balancer,
 it may be required to use the X-Forwarded-For (XFF) header instead of the origin
-IP address. This can be configured as an option on the home server like so:
+IP address. This can be configured as an option on the home server like so::
 
   captcha_ip_origin_is_x_forwarded: true
-