Yeah, the GitHub robots.txt is surprisingly restrictive:
User-agent: *
Disallow: /*/pulse
Disallow: /*/tree/
That "/*/tree" rule means that search engine crawlers are allowed to hit the README file of a repo but effectively NONE of the other files in it.Which means that if you keep your project documentation on GitHub in a docs/ folder it won't be indexed!
You need to publish it to a separate site via GitHub Pages, or use https://readthedocs.org/
(Side note: I just noticed https://github.com/ekansa/Open-Context-Data is explicitly listed in the robots.txt for GitHub - the only repo that gets a mention like that. I'd love to know the story behind that!)