asyncio: add a note about (non) thread safety in each class
diff --git a/Doc/library/asyncio-stream.rst b/Doc/library/asyncio-stream.rst
index 22b7341..41b24ac 100644
--- a/Doc/library/asyncio-stream.rst
+++ b/Doc/library/asyncio-stream.rst
@@ -85,6 +85,8 @@
 
 .. class:: StreamReader(limit=None, loop=None)
 
+   This class is :ref:`not thread safe <asyncio-multithreading>`.
+
    .. method:: exception()
 
       Get the exception.
@@ -155,6 +157,8 @@
    wait for flow control.  It also adds a transport attribute which references
    the :class:`Transport` directly.
 
+   This class is :ref:`not thread safe <asyncio-multithreading>`.
+
    .. attribute:: transport
 
       Transport.