Document how to mark additional tests as skipped

[danielbachhuber]

At times, a host may find a test is failing for some known reason. They should be able to mark the test as skipped in their own test runner instance.

Related #47

[danielbachhuber]

As it turns out, there's no CLI argument for skipping specific tests, only groups :/

It may be possible by passing regex to --filter

[timiwahalahti]

Just started setting up our automated tests and ran into the #202. Because of that test failing, I would not wan to start our automation as it provides incorrect results (the failure is because of the test itself, not because of the environment) and spams us the failure every time.

It would be neat to have a way to skip that test altogether until it is fixed.