future_moves: add comment regarding no-move

src/logic/future_moves.rs

@@ -222,6 +222,8 @@ impl FutureMoves {
             })
             .collect();
 
+        // if there are no moves to take, making
+        // no move is also an option!
         if new.is_empty() {
             new.push(Move::new(None, parent_board, new_color, self.agent_color));
         }