Update readme.

Author: WaVEV

README.md

@@ -114,8 +114,7 @@ from the new application's `apps.py` file.
 - `QuerySet.delete()` and `update()` do not support queries that span multiple
   collections.
 
-- `Subquery`, `Exists`, and using a `QuerySet` in `QuerySet.annotate()` aren't
-  supported.
+- `QuerySet` in `QuerySet.annotate()` aren't supported.
 
 - `DateTimeField` doesn't support microsecond precision, and correspondingly,
   `DurationField` stores milliseconds rather than microseconds.