[gnome-chess] Add warning comment about the Seven Tag Roster

[Michael Catanzaro <mcatanzaro src gnome org>]

commit d8d14506aeddaba64886f5af80c976b270d1b704
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Fri Dec 4 18:04:23 2020 -0600

    Add warning comment about the Seven Tag Roster

 lib/chess-pgn.vala | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/lib/chess-pgn.vala b/lib/chess-pgn.vala
index 4e927a5..09582b9 100644
--- a/lib/chess-pgn.vala
+++ b/lib/chess-pgn.vala
@@ -10,6 +10,7 @@
  * license.
  */
 
+/* This is the Seven Tag Roster (STR). They have to appear at the top, in this order. */
 private int str_index (string name)
 {
     if (name == "Event")