Validate examples in configuration.md

[meowjesty]

The Configuration page now has a bunch of examples, but they're not validated against anything, so if we add new stuff, or make changes the examples would be silently giving out wrong information.

I can think of a couple of ways to solve this:

1. Leverage Rust documentation tests to load our config examples and check if they're valid;
2. Use our documentation extraction tool (medschool) to spit out the examples, and validate the json we get;

Which one would be easier? Also, anyone can think of other approaches?

[aviramha]

I think we should add a "mirrord validate" command then we can use it here also, later on we can use it in the extension to verify before launching.