To be completely honest, Dimitry, I would not send the program an email. It may hurt or help you -- nobody knows. It can help you in that that residency program may value your experience. But it can hurt you in that the devil's advocate would question it -- if this experience was so impt, why didn't the applicant put it in his/her app the first time? or why did he/she not wait to include it in the app before submitting? once the devil advocate figures out that you mistakenly thought you could edit your CV after submission, then that would look bad on your part because it would reflect a hint of carelessness.
just giving you perspectives on both sides.
the reason why i would not send the program an email is beacuse in EM, they are more likely to select you for an interview likely due to other things on your app (Grades, scores, etc) rather than based on one particular experience that you have. if like one paragraph of your PS was missing, that is something that you need to email programs about, even though that would still show carelessnes on your self.
don't panic about interview invites yet. most go out in the 1st week of november. i know it gives you an uneasy feeling of knowing that you applied without having a "complete" application, but unfortunately, i think that's the best way to approach this. i don't think that experience can make or break you for the invite, but after the interview, it may help you during the ranking process; but again, once you get the interview, mention this experience there and that will be factored in.