Add some informations about current game problems inside the game

[fabio]

So that users won't complain again and again about them in the forum (e.g. "the game lags"). A list of problems was already reported on the forum, see http://www.wildfiregames.com/forum/index.php?showtopic=15796&st=0&p=236295&fromsearch=1&#entry236295 .

Ideally there should be a brief list of major problems and a TODO list (as it was available in past releases announce).