updated description of test metadata to match current testharness.js

testharness.js complains at you if you don't use an email address for the author metadata, and also if you don't put metadata for a file with multiple tests in the <head>.  Updated the tutorial to reflect this and give an example.
This warns just the same:

> Metadata property "author" for test: … must have name and contact information ("name <email>" or "name http(s)://")