Update source/faq/diagnostics.txt

Fixed improper interrogative: Why => What

Signed-off-by: Sam Kleinman <samk@10gen.com>

source/faq/diagnostics.txt

@@ -269,8 +269,8 @@ In the worst case, you may have to consider re-sharding your data
 and :ref:`choosing a different shard key <sharding-internals-choose-shard-key>`
 to correct this pattern.
 
-Why can prevent a sharded cluster from balancing?
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+What can prevent a sharded cluster from balancing?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 If you have just deployed your sharded cluster, you may want to
 consider the :ref:`troubleshooting suggestions for a new cluster where
@@ -321,7 +321,7 @@ consider the following options, depending on the nature of the impact:
      to limit the size of the migration.
 
    - Your cluster may be over capacity, and you may want to attempt to
-     :ref:`add one or two shards <sharding-procedure-add-shard>` to
+     :ref:`add one or two shards <sharding-procedure-add-shardt>` to
      the cluster to distribute load.
 
 It's also possible that your shard key causes your