Add a section on testing of Infrastructure as Code (IaC) 

As more and more (web) applications are shipped as containers or based on IaC, I think we should add a section on the specifics testing IaC configurations/systems and container (e.g., Docker) setups. It needs to be decided how much into the details we want to go (e.g., this could be a rather high-level section on best practices or multiple sections discussing the details).

Cheers,
Achim