Documentation for `.sydtest.yaml`

Hello! I was looking for a way to pass some arguments (`--no-randomize-execution-order`) automatically without writing a bash script or Makefile. Thus, I have ended up with adding the parameter into `.sydtest.yaml`: ```yaml randomize-execution-order: false ``` Probably it will be useful to mention this feature somewhere unless it's not part of the public API. For example `HSpec` mentions this about `.hspec` file here: https://hspec.github.io/options.html