jwt : update comment

git-svn-id: https://svn.fournier38.fr/svn/ProgSVN/trunk@5294 bf3deb0d-5f1a-0410-827f-c0cc1f45334c

jwt.php

@@ -159,6 +159,8 @@ class jwt
   // }}}
 
   /** Return the provided string in base64 without equal at the end
+    * To be URL compliant, the slash and plus are converted to underscore and
+    * dash
     * @param string $str The string the convert in base64
     * @return string The string converted in base64
     */