style: fixing code block identification

Author: Sam Kleinman

source/reference/method/sh.addShard.txt

@@ -10,14 +10,16 @@ sh.addShard()
                        replica set configuration.
 
    Use this method to add a database instance or replica set to a
-   :term:`sharded cluster`.
-   This method must be run on a :program:`mongos` instance.
-   The ``host`` parameter can be in any of the following forms: ::
-
-        [hostname]
-        [hostname]:[port]
-        [set]/[hostname]
-        [set]/[hostname],[hostname]:port
+   :term:`sharded cluster`. This method must be run on a
+   :program:`mongos` instance. The ``host`` parameter can be in any
+   of the following forms:
+
+   .. code-block:: none
+
+      [hostname]
+      [hostname]:[port]
+      [set]/[hostname]
+      [set]/[hostname],[hostname]:port
 
    You can specify shards using the hostname, or a hostname and port
    combination if the shard is running on a non-standard port.