Most online applications ask if you have, or think you may have, a disability. So, by the time you've gotten to the interview, chances are they already know. If not though, you can perhaps mention it in your achievements. Say something like "I'm really proud of how well I've done in school and in previous jobs, despite having dyslexia." or something along those lines. They'll see that you don't let anything get the better of you and it shows that you can work hard despite handicaps.