That's a lot to put on a sticker -- people aren't going to read that. Maybe something a bit snappier, e.g. "Freelance coder: available for gigs" or something.

I would question, however, whether putting a sticker of any kind is gonna help you score gigs. I mean, if you were looking for a coder, would you really approach some random guy/gal in a coffee shop based solely on a sticker on their laptop and knowing nothing else about them?

Maybe having a sticker with a link to your github, as suggested by others, would be more useful (if your user id is memorable).