Suggests configuration file should be the default "way" with `verify.py`

In this merge request, the idea is we emphasize people should rather use configuration files with verify.py. The change is minor, but allows users to run the script issuing:

$ ./bin/verify.py -vv <my-config>

I mark it as a work-in-progress, because I still wanted to have <my-config> to optionally be a resource. @mguenther: could you please make so? I'm not sure I'm capable of doing this with ruining something else. This will allow us to distribute baselines inside packages, w/o requiring users to know where they are installed.