I added cppreference.com now and kicked off a crawl. It'll be a while. The list of domains is pretty small right now -- it was intended to be bigger before the announcement was made. Will also add RFCs and man pages soon.

There will (soon) be a form to request new domains are added to the index, so if there are any sites you want indexed which are outside of my personal expertise, then you'll be able to request them.