Adapt CWL links to external resources

[Brilator]

Some parts in the Workflow Description point to CWL docs incl. their user guide, which may be more volatile than a versioned specification.

Although their user guide is more comprehensible, I would suggest to replace external references with ones to their specification and / or / partly reproduce the explanations.

One example: "processing unit" is not called / searchable like this in CWL. So it should be explained in the ARC specification.