Explain the win condition on the ready-up screen

Players had no in-game indication of what actually ends the game
before reaching the terminal itself.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/game/waiting.html.twig

@@ -13,6 +13,8 @@
                 <h4>{{ session.game.name }}</h4>
                 <p>Welcome to the game! Please wait for all players to join and signal they are ready to start.</p>
 
+                <p>This game will end when you disable the virus by having its source files deleted from the server.</p>
+
                 <div class="game-info">
                     Please keep the following things in mind:
                     <ul>