There is no standard format as far as I know. People treat ingame biographies in roughly three ways:
- a full IC way where whatever is written there is what the character would write in their intro
- a database result that would come up with a search someone would be interested to run it
- a fully OOC story or link to one.
I personally prefer the first but the intent of the player is usually clear from how they write theirs so it does not matter.