1) Link github into my site graph. Long ago when I filled out my profile I put my homepage into github, and that already created the relevant link. github++.
2) Link my homepage to my Google Profile.
2a) Added the following to my homepage:
<link rel='me' href='http://www.google.com/profiles/evan.martin'>
2b) Recrawled the site with https://sgapi-recrawl.appspot.com/
3) Link from my profile back to github. Clicked "edit" on my profile, added the github link manually. After creating it, click "edit", there's a checkbox to say "this is me".
4) Now in Buzz I can click "Connected Sites" and it show the github URL as a source for updates.
github → homepage
homepage → google profile
google profile → github
was enough to convince the social graph API that the github link is legit.
This all seems rather complicated. I believe it will be made easier in the future (sgapi-recrawl was a quick hack), and also that by providing incentives for site owners to create "me" links, sites in the future will magically have access to your site graph without typing any URLs.
I found this social graph queryer helpful for testing while getting things going.