Update rules info box

[Herkarl]

• Write down unspoken rules
• Clarify that you should use tags instead of removing slides
• Write down alcohol rules clearly

Possibly make rules appear as something like a popup to make sure that they are read

[hexakon]

METAdorerna said that people do practice common sense. What needs adding however are clarifications on allowed file formats

[foodelevator]

It sometimes (well I know it has happened once. perhaps that's not "sometimes" ^^) happens that people who aren't familiar with the system deletes all other slides instead of using tags.
Perhaps that could be clarified a bit more, but I'm not 100% sure.