Improve GitHub forks discoverability

Quite often a repo appears inactive when there is actually active development going on that isn't plainly visible on the front page. I ALWAYS tell people that the single most valuable feature for dealing with old repos is the network graph: https://github.com/isaacs/github/network

This graph enables me to immediately grok if there is perhaps a far more active and up-to-date fork, if perhaps a bug or feature that seems to have been open forever is actually resolved by someone else, if a repo has potential to merge pull-requests, yet people who fork are neglecting to open them, or even if the repo is in fact under active development for a new release and you just want to find out which branch is most active (their dev branch) in case the master branch or front-page branch gets little activity.

For this reason, I've wanted to see a feature that suggests or brings attention to alternative forks, that coincides with the network graph. It would have to be designed appropriately so as not to detract from the primary repo, but at the very least provide a self-updating hint towards alternative resources people could use when they come up short on inactive projects.

I believe this would be a better alternative to #144