The way I know it, there are two ways of getting a resume on IMDb.
One is, just like David said, to have a feature on IMDb, then your credit will show up. (Even with a short that was in at least one festival, if the producer added the credits for it, then your resume will be created then.)
The other is to pay to get it on there, and you have to do all the work of adding your stuff in. I personally do not agree with that, cause that way anyone can put anything on there.