Vulnerability Scanning

I think it might be useful to have a section regarding vulnerability scanners; I'm not totally sure that any of them would fit into any of the existing categories (maybe in testing)? The tools I had in mind are the following:

- OpenVAS - https://github.com/greenbone/openvas-scanner
- Clair - https://github.com/coreos/clair

If this seems like a good idea I'd be happy to create a PR.