Simplify enabling recaptcha instructions a bit

docs/configuring-captcha.md

@@ -2,7 +2,7 @@
 
 # Overview
 Captcha can be enabled for this home server. This file explains how to do that.
-The captcha mechanism used is Google's ReCaptcha. This requires API keys from Google.
+The captcha mechanism used is Google's [ReCaptcha](https://www.google.com/recaptcha/). This requires API keys from Google.
 
 ## Getting keys
 
@@ -10,15 +10,14 @@ Requires a site/secret key pair from:
 
 <http://www.google.com/recaptcha/admin>
 
-Must be a reCAPTCHA v2 key using the "I'm not a robot" Checkbox option
+Must be a reCAPTCHA **v2** key using the "I'm not a robot" Checkbox option
 
 ## Setting ReCaptcha Keys
 
 Once registered as above, set the following values:
 
+```yaml
+matrix_synapse_enable_registration_captcha: true
 matrix_synapse_recaptcha_public_key: 'YOUR_SITE_KEY'
 matrix_synapse_recaptcha_private_key: 'YOUR_SECRET_KEY'
-
+```
-In addition, you MUST enable captchas via:
-
-    matrix_synapse_enable_registration_captcha: true