DOCS-12039 Document valid values for cursorTimeoutMillis parameter

Author: Isabella Siu

source/reference/parameters.txt

@@ -531,6 +531,13 @@ General Parameters
 
       db.adminCommand( { setParameter: 1, cursorTimeoutMillis: 300000 } )
 
+   Setting :parameter:`cursorTimeoutMillis` to less than or equal
+   to ``0`` results in all cursors being immediately eligible for timeout.
+   Generally, the timeout value should be greater than the average amount of
+   time for a query to return results. Use tools like the :method:`cursor.explain()`
+   cursor modifier to analyze the average query time and select an appropriate
+   timeout period. 
+
 .. parameter:: failIndexKeyTooLong
 
    .. versionadded:: 2.6