Translation:The participants will be informed of the rules.
I think "informed of the rules" is much more natural than "informed about the rules."
But, I actually looked up which came up on google more often. "informed of" generated 46.1 million links, while "informed about" generated 41.4 million links, so not that big a difference (the first links in each case were to grammar pages saying both prepositions were acceptable).
In the immediately preceding question, which was the same but for masculine participants (Les participants seront informé des règles), DL missed the “s” off “informés”, so I did the same here and was marked as incorrect. So that’s two of todays’s five Health “lives” lost in one exercise through no fault of my own. Grrr! DL French is such a mess.