Update doc

lib/includes/nghttp2/nghttp2.h

@@ -3023,10 +3023,10 @@ nghttp2_session_get_stream_effective_local_window_size(nghttp2_session *session,
 /**
  * @function
  *
- * Returns the amount of data that the remote endpoint can send
- * without receiving stream level WINDOW_UPDATE frame.  It is also
- * subject to the connection level flow control.  So the actual amount
- * of data to send is
+ * Returns the amount of flow-controlled payload (e.g., DATA) that the
+ * remote endpoint can send without receiving stream level
+ * WINDOW_UPDATE frame.  It is also subject to the connection level
+ * flow control.  So the actual amount of data to send is
  * min(`nghttp2_session_get_stream_local_window_size()`,
  * `nghttp2_session_get_local_window_size()`).
  *
@@ -3076,9 +3076,10 @@ nghttp2_session_get_effective_local_window_size(nghttp2_session *session);
 /**
  * @function
  *
- * Returns the amount of data that the remote endpoint can send
- * without receiving connection level WINDOW_UPDATE frame.  Note that
- * each stream is still subject to the stream level flow control (see
+ * Returns the amount of flow-controlled payload (e.g., DATA) that the
+ * remote endpoint can send without receiving connection level
+ * WINDOW_UPDATE frame.  Note that each stream is still subject to the
+ * stream level flow control (see
  * `nghttp2_session_get_stream_local_window_size()`).
  *
  * This function returns -1 if it fails.