Add explanation of regex-based consent.disable

modules/consent/docs/consent.md

@@ -232,6 +232,21 @@ Disable consent for some IdPs for a given SP:
         ),
     ),
 
+### Regular expression support ###
+
+You can use regular expressions to evaluate the entityId of either the IdP
+or the SP.  It makes it easy to disable consent for an entire domain or
+for a range of specific entityIds.  Just use an array instead of a flat string
+with the following format (note that flat string and array entries are allowed
+at the same time) :
+
+    $metadata['https://sp.example.org'] = array(
+        [...]
+        'consent.disable' => array(
+            'https://idp1.example.org/',
+            array('type'=>'regex', 'pattern'=>'/.*\.mycompany\.com.*/i',
+        ),
+    ),
 
 Attribute presentation
 ----------------------