doc: missing :: at end of line before example code.

Author: rouilj

roundup/cgi/templating.py

@@ -3758,7 +3758,7 @@ def readfile(self, name, optional=False):
            file where you can use linters/minifiers and other
            tools on it.
 
-           A TAL example:
+           A TAL example::
 
              <script tal:attributes="nonce request/client/client_nonce"
              tal:content="python:utils.readfile('mylibrary.js')"></script>