I don't think you need to report that during your OPT application. I didn't even have a job when I applied for my OPT. During OPT, You can do multiple gigs, volunteer (at least 20 hours), work part time or be self employed [All in your field of study] . For self employed, I think you have to show that you're working close to 40 hours(full time) a week. As long as you report your changes to your international advisor within ten days,  you're all set.