Well no, that’s how you should be able to do it, but linking my GitHub never seemed to work for me. And you’ll also notice my GitHub uses a different pic. I also never got the GitHub contributor title despite having contributed to the code.
The way I did it comes with an interesting story. I actually exploited a bug in discourse that has since been closed. It’s a fun read here: Custom avatars on forum
But don’t get your hopes up, I didn’t describe the method and @pac reported the bug responsibly to discourse so they could fix it.