Issue #28089: Document TCP_NODELAY in asyncio

Initial patch by Mariatta Wijaya.
(grafted from 853e3f4d6cd98ac4590238bc1c60e40fd8ed3895)
diff --git a/Doc/library/asyncio-protocol.rst b/Doc/library/asyncio-protocol.rst
index c0342f7..3fbf510 100644
--- a/Doc/library/asyncio-protocol.rst
+++ b/Doc/library/asyncio-protocol.rst
@@ -25,6 +25,9 @@
 
 The transport classes are :ref:`not thread safe <asyncio-multithreading>`.
 
+.. versionchanged:: 3.6
+   The socket option ``TCP_NODELAY`` is now set by default.
+
 
 BaseTransport
 -------------