I'm not going to post mine here as I don't know if it's against any TOS but if a moderator could chime in... Maybe there is a better place or way to do it?
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I link mine in my signature.
I haven't used Instagram but what I see would make it similar to face book. We don't have a place to store it in the profile so a possible place to put it would be personal web site if it's in the form of a URL. The other option would be to include it in your signature. In your signature it can be removed should you change your mind about it in the future.