Adds code comments to CrossDomainObject test
Adds code comments to CrossDomainObject test

Addresses comment:
lostmu: Add a comment explaining the intent of this method or extract
this code into a separate method with clear name.
https://github.com/pythonnet/pythonnet/pull/958/#discussion_r390644281

AlexCatarino/pythonnet,AlexCatarino/pythonnet,QuantConnect/pythonnet,QuantConnect/pythonnet,AlexCatarino/pythonnet,pythonnet/pythonnet,pythonnet/pythonnet,pythonnet/pythonnet,AlexCatarino/pythonnet,QuantConnect/pythonnet