create a video for testing for demo mode

[meleu]

maybe adapting this forum post for a doc page: http://retroachievements.org/viewtopic.php?t=81

update

It would be cool if we had a video showing techniques to find the RAM address for demo mode. In some games it's really easy to find, but in other's it can be tricky. The video should show examples on various games, the simple and the complex ones.