Document CetusGuard as a Docker socket proxy solution

[hectorm]

Hi, I'm the author of CetusGuard, a Docker socket proxy that can be used by the Netdata agent to securely communicate with the Docker daemon.

Here is an example deployment with Docker Compose that only gives the Netdata agent container read access to a single Docker daemon API endpoint.

I was wondering if you are open to accept a pull request in the docs mentioning this solution.