docs: Add asyncio source code links (GH-16640)

diff --git a/Doc/library/asyncio-platforms.rst b/Doc/library/asyncio-platforms.rst
index 7e4a70f..390ee19 100644
--- a/Doc/library/asyncio-platforms.rst
+++ b/Doc/library/asyncio-platforms.rst
@@ -23,6 +23,12 @@
 Windows
 =======
 
+**Source code:** :source:`Lib/asyncio/proactor_events.py`,
+:source:`Lib/asyncio/windows_events.py`,
+:source:`Lib/asyncio/windows_utils.py`
+
+--------------------------------------
+
 .. versionchanged:: 3.8
 
    On Windows, :class:`ProactorEventLoop` is now the default event loop.