Add type annotation in comments

src/python/grpcio/grpc/_cython/_cygrpc/aio/completion_queue.pxd.pxi

@@ -52,18 +52,18 @@ cdef class BaseCompletionQueue:
 
 cdef class _BoundEventLoop:
     cdef readonly object loop
-    cdef readonly object read_socket
+    cdef readonly object read_socket  # socket.socket
 
 
 cdef class PollerCompletionQueue(BaseCompletionQueue):
     cdef bint _shutdown
     cdef cpp_event_queue _queue
     cdef mutex _queue_mutex
-    cdef object _poller_thread
+    cdef object _poller_thread  # threading.Thread
     cdef int _write_fd
-    cdef object _read_socket
-    cdef object _write_socket
-    cdef dict _loops
+    cdef object _read_socket    # socket.socket
+    cdef object _write_socket   # socket.socket
+    cdef dict _loops            # Mapping[asyncio.AbstractLoop, _BoundEventLoop]
 
     cdef void _poll(self) nogil
     cdef shutdown(self)