(DOCSP-35695): Update optimization info for lookup (#5857) (#5868)

* (DOCSP-35695): Update optimization info for lookup

* consistency

* wording

* edits

* review edit

* tech review edits

Author: jeff-allen-mongo

source/reference/operator/aggregation/lookup.txt

@@ -468,22 +468,29 @@ different ``$lookup`` operations.
 
        - ``$lookup`` operations that perform equality matches with a
          single join typically perform better when the source collection
-         contains an index on the ``foreignField``.
+         contains an index on the ``localField``.
 
-   * - :ref:`Uncorrelated Subqueries<lookup-uncorrelated-subquery>`
+       - An index on the ``foreignField`` in the foreign collection
+         cannot support an equality match with a single join.
 
-     - .. _uncorrelated-subqueries-performance: 
+   * - :ref:`Uncorrelated Subqueries <lookup-uncorrelated-subquery>`
 
-       - ``$lookup`` operations that contain uncorrelated subqueries
-         typically perform better when the inner pipeline can reference
-         an index on the ``foreignField``. 
+     - .. _uncorrelated-subqueries-performance:
+     
+       - An index on the foreign collection cannot support uncorrelated
+         subqueries.
+      
+       - To improve performance for uncorrelated subqueries, use generic
+         indexing strategies and query optimization techniques. For
+         example, add appropriate indexes to support aggregation stages
+         before ``$lookup``.
 
        - MongoDB only needs to run the ``$lookup`` subquery once before
          caching the query because there is no relationship between the
-         source and foreign collections. The ``$lookup`` subquery is not
-         based on any value in the source collection. This behavior
-         improves performance for subsequent executions of this query.
-
+         source and foreign collections. The subquery is not based on
+         any value in the source collection. This behavior improves
+         performance for subsequent executions of the ``$lookup``
+         operation.
 
    * - :ref:`Correlated Subqueries <lookup-concise-correlated-subquery>`
 
@@ -622,7 +629,7 @@ The operation corresponds to this pseudo-SQL statement:
    );
 
 For more information, see
-:ref:`Equality Match Performance Considerations<equality-match-performance>`. 
+:ref:`Equality Match Performance Considerations <equality-match-performance>`. 
 
 .. _unwind-example: