Add brief documentation and example for junit-5 parameterized tests

[lukasjelonek]

Motivation:

Document the usage of parameterized tests with junit 5 and vertx. See #78

Conformance:

Your commits should be signed and you should have signed the Eclipse Contributor Agreement as explained in https://github.com/eclipse/vert.x/blob/master/CONTRIBUTING.md Please also make sure you adhere to the code style guidelines: https://github.com/vert-x3/wiki/wiki/Vert.x-code-style-guidelines

[jponge]

Thanks!