Add documentation

[rjaegers]

amp-cucumber-cpp-runner could do with some documentation on how to start using it in your own project.

I think at least the README should be updated with customer-first documentation on top, and development (e.g. working on amp-cucumber-cpp-runner itself) documentation at the bottom, clearly separated.

Next start using the Wiki might help. I had a recent inquiry about using amp-cucumber-cpp-runner with CTest as a driver, in that scenario the hooks did not seem to work. But what was missing was a dependency set_tests_properties(MyTest PROPERTIES DEPENDS my_test_runner)