minor: refactor release notes

Author: Bob Grabar

source/release-notes/2.2.txt

@@ -90,7 +90,7 @@ We recommend the following upgrade procedure for a sharded cluster:
   a time* using the :ref:`stand alone <2.2-upgrade-standalone>` procedure.  
   When you have *fewer* than *three* config servers active, the cluster 
   metadata will be read-only which will prevent (and abort)
-  all chunk migrations and chunk splits. 
+  all chunk migrations and chunk splits.
 
 - Upgrade all remaining cluster components, using the :ref:`upgrade
   procedure for replica sets <2.2-upgrade-replica-set>` for each of
@@ -104,9 +104,8 @@ upgrade the mongos instances, config servers, and shards in any order.
 
 .. note::
 
-   Balancing does not currently work in *mixed* 2.0.x and 2.2.0 deployments. 
-
-
+   Balancing does not currently work in *mixed* 2.0.x and 2.2.0
+   deployments. See :issue:`SERVER-6902` for more information.
 
 Changes
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