Hi there,

It seems that "connect_read_pipe" is not implemented in ProactorEventLoop. Does it make sense to update docs in these places?
- https://docs.python.org/3/library/asyncio-platforms.html#windows
- https://docs.python.org/3/library/asyncio-eventloop.html#working-with-pipes 

Or, this is a bug?

# The code to reproduce

```
import asyncio
import sys


async def read_stdin():
    reader = asyncio.StreamReader()
    protocol = asyncio.StreamReaderProtocol(reader)
    await asyncio.get_running_loop().connect_read_pipe(lambda: protocol, sys.stdin)
    while True:
        line = await reader.readline()
        print("stdin > ", line)


async def main():
    task = asyncio.create_task(read_stdin())
    await asyncio.sleep(5)
    task.cancel()


if __name__ == "__main__":
    asyncio.run(main())
```

P.S: The "loop.add_reader()" raises "NotImplementedError" which is clear according to the docs.

Thanks in advance!

# Log

```
C:\Users\USER>.platformio\python3\python.exe test.py
Exception in callback _ProactorReadPipeTransport._loop_reading()
handle: <Handle _ProactorReadPipeTransport._loop_reading()>
Traceback (most recent call last):
  File "C:\Users\USER\.platformio\python3\lib\asyncio\proactor_events.py", line 299, in _loop_reading
    self._read_fut = self._loop._proactor.recv(self._sock, 32768)
  File "C:\Users\USER\.platformio\python3\lib\asyncio\windows_events.py", line 445, in recv
    self._register_with_iocp(conn)
  File "C:\Users\USER\.platformio\python3\lib\asyncio\windows_events.py", line 718, in _register_with_iocp
    _overlapped.CreateIoCompletionPort(obj.fileno(), self._iocp, 0, 0)
OSError: [WinError 6] The handle is invalid

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\USER\.platformio\python3\lib\asyncio\events.py", line 80, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\USER\.platformio\python3\lib\asyncio\proactor_events.py", line 309, in _loop_reading
    self._fatal_error(exc, 'Fatal read error on pipe transport')
  File "C:\Users\USER\.platformio\python3\lib\asyncio\proactor_events.py", line 131, in _fatal_error
    self._force_close(exc)
  File "C:\Users\USER\.platformio\python3\lib\asyncio\proactor_events.py", line 134, in _force_close
    if self._empty_waiter is not None and not self._empty_waiter.done():
AttributeError: '_ProactorReadPipeTransport' object has no attribute '_empty_waiter'
Exception ignored in: <function _ProactorBasePipeTransport.__del__ at 0x000002181B927A60>
Traceback (most recent call last):
  File "C:\Users\USER\.platformio\python3\lib\asyncio\proactor_events.py", line 116, in __del__
    self.close()
  File "C:\Users\USER\.platformio\python3\lib\asyncio\proactor_events.py", line 108, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "C:\Users\USER\.platformio\python3\lib\asyncio\base_events.py", line 746, in call_soon
    self._check_closed()
  File "C:\Users\USER\.platformio\python3\lib\asyncio\base_events.py", line 510, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
```