tests/README.md Add note on scheduling.

uasyncio_iostream/tests/README.md

@@ -16,3 +16,13 @@ iotest.py Measure timing of I/O scheduling with a scope.
 auart.py Run a loopback test on a physical UART.  
 auart_hd.py Simulate a pair of devices running a half-duplex protocol over a
 pair of UARTs.
+
+# Note on I/O scheduling
+
+Examination of the code, along with running iotest.py, demonstrates that I/O
+polling does not take place as frequently as it could. In the presence of coros
+which issue `yield asyncio.sleep(0)` polling occurs when all such coros have
+run.
+
+An option is to modify `core.py` to schedule I/O after each coro has run - the
+drawback being a reduced rate at which these round-robin tasks are scheduled.