DOCSP-13748 clarify numInitialChunk meaning

Author: npentrel

source/reference/command/shardCollection.txt

@@ -101,11 +101,11 @@ Definition
 
         - integer
 
-        - Specifies the number of chunks to create
-          initially when sharding an *empty* collection with a
+        - Specifies the initial number of chunks to create across all shards in 
+          the cluster when sharding an *empty* collection with a
           :ref:`hashed shard key <sharding-hashed-sharding>`. MongoDB
           will then create and balance chunks across the cluster. The
-          ``numInitialChunks`` must be less than ``8192`` per shard.
+          ``numInitialChunks`` must result in less than ``8192`` per shard.
 
           If the collection is not empty or the shard key does not
           contain a hashed field, the operation returns an error.