added note

src/main.rs

@@ -62,6 +62,7 @@ fn calculate_options() -> Result<(), &'static str> {
     // We know how many possibilities there are the first round...
     game.do_move(GameMove(1, Tile::Blue, 0))?;
     // We also know how many possiblities there are the second round.
+    // NB: THIS STEP INTRODUCES ERROR, THE REAL NUMBER WILL BE SMALLER THAN THIS
     game.do_move(GameMove(0, Tile::Yellow, 0))?;
 
     let options = count_options(game, 0, 4);