DOCS-920 getShardDistribution method, including sample output

Author: kay-kim

source/reference/method/db.collection.getShardDistribution.txt

@@ -93,6 +93,26 @@ db.collection.getShardDistribution()
      returns the average object size, including the unit of measure,
      for the shard.
 
+   For example, the following is a sample output for the distribution
+   of a sharded collection:
+
+   .. code-block:: sh
+
+      Shard shard-a at shard-a/MyMachine.local:30000,MyMachine.local:30001,MyMachine.local:30002
+      data : 38.14Mb docs : 1000003 chunks : 2
+      estimated data per chunk : 19.07Mb
+      estimated docs per chunk : 500001
+
+      Shard shard-b at shard-b/MyMachine.local:30100,MyMachine.local:30101,MyMachine.local:30102
+      data : 38.14Mb docs : 999999 chunks : 3
+      estimated data per chunk : 12.71Mb
+      estimated docs per chunk : 333333
+
+      Totals
+      data : 76.29Mb docs : 2000002 chunks : 5
+      Shard shard-a contains 50% data, 50% docs in cluster, avg obj size on shard : 40b
+      Shard shard-b contains 49.99% data, 49.99% docs in cluster, avg obj size on shard : 40b
+
    .. seealso:: :doc:`/sharding`
 
 .. COMMENT -- not sure if I should mention the source of the data: