DOCSP-13551: [MONGOSH] Support readConcern on cursor

Author: steveren

source/reference/methods.txt

@@ -509,6 +509,10 @@ Cursor Methods
 
      - Returns the number of documents left in the current cursor batch.
 
+   * - :method:`cursor.readConcern()`
+
+     - Specifies a :term:`read concern` for a :method:`find()` operation.
+
    * - :method:`cursor.readPref()`
 
      - Specifies a :term:`read preference` to a cursor to control how