DOCS-16476 Resharding a unique collection (#5191)

* First draft'

* Copy edits

Author: nvillahermosa-mdb

source/core/sharding-reshard-a-collection.txt

@@ -148,10 +148,10 @@ Limitations
 
 - Only one collection can be resharded at a time.
 - :rsconf:`writeConcernMajorityJournalDefault` must be ``true``.
-- Resharding a collection that has a
-  :ref:`uniqueness <index-type-unique>` constraint is not supported.
-- The new shard key cannot have a :ref:`uniqueness <index-type-unique>`
-  constraint.
+- To reshard a collection that has a :ref:`uniqueness
+  <index-type-unique>` constraint, the new shard key must satisfy
+  the :ref:`unique index requirements <sharding-shard-key-unique>` for 
+  any existing unique indexes.
 - The following commands and corresponding shell methods are not
   supported on the collection that is being resharded while the
   resharding operation is in progress: