improve API documentation for opening new streams

interface.go

@@ -121,6 +121,8 @@ type Session interface {
 	AcceptUniStream() (ReceiveStream, error)
 	// OpenStream opens a new bidirectional QUIC stream.
 	// It returns a special error when the peer's concurrent stream limit is reached.
+	// There is no signaling to the peer about new streams:
+	// The peer can only accept the stream after data has been sent on the stream.
 	// TODO(#1152): Enable testing for the special error
 	OpenStream() (Stream, error)
 	// OpenStreamSync opens a new bidirectional QUIC stream.