bpo-33649: Add high-level APIs cheat-sheet (GH-9319)

diff --git a/Doc/library/asyncio-sync.rst b/Doc/library/asyncio-sync.rst
index 8da5aa8..f299885 100644
--- a/Doc/library/asyncio-sync.rst
+++ b/Doc/library/asyncio-sync.rst
@@ -94,6 +94,8 @@
    :meth:`clear` method.  The :meth:`wait` method blocks until the
    flag is set to *true*.  The flag is set to *false* initially.
 
+   .. _asyncio_example_sync_event:
+
    Example::
 
       async def waiter(event):