DOCS-13725 update cursor snapshot documentation

Author: npentrel

source/includes/extracts-concurrency-consistency-recency.yaml

@@ -106,12 +106,12 @@ content: |
    change the indexed field on the index used by the query; then the
    cursor will return the same document more than once.
 
-   If your collection has a field or fields that are
-   never modified, you can use a *unique* index on this field or these
-   fields so that the query will return each document no more than
-   once. Query with :method:`~cursor.hint()` to explicitly force the
-   query to use that index.
-   
+   Queries that use :ref:`unique indexes <index-type-unique>` can, in
+   some cases, return duplicate values. If a cursor using a unique index
+   interleaves with a delete and insert of documents sharing the same
+   unique value, the cursor may return the same unique value twice from
+   different documents.
+
 ---
 ref: lock-general
 content: |