Inaccessible references to sgdev.org in documentation

Created by: ianlopshire

There are many references to sgdev.org in the documentation contained in this repo that are not accessible to people outside of Sourcegraph. The architecture.md page is particularly bad.

I believe all of sourcegraph.sgdev.org/github.com links could be replaced with their github.com equivalents. I'd be happy to submit a PR if that is the case.