minor: reference material checkup

Author: Sam Kleinman

source/reference/command/movePrimary.txt

@@ -10,7 +10,7 @@ movePrimary
    primary shard. The primary shard for a database holds all
    un-sharded collections in the database. :dbcommand:`movePrimary`
    is an administrative command that is only available for
-   :program:`mongos` instances and is intended to be used when
+   :program:`mongos` instances. Only use :dbcommand:`movePrimary` when
    removing a shard from a shard cluster.
 
    :dbcommand:`movePrimary` changes the primary shard for this

source/reference/method/db.createCollection.txt

@@ -55,7 +55,7 @@ db.createCollection()
       db.createCollection("people", { size: 2147483648 })
 
    This command provides a wrapper around the database command
-   ":dbcommand:`create`. See the ":wiki:`Capped Collections <Capped+Collections>`"
+   :dbcommand:`create`. See the ":wiki:`Capped Collections <Capped+Collections>`"
    wiki page for more information about capped collections.
 
    .. STUB :doc:`/core/capped-collections`"