Update README.md

Update deduplicating test code example to:

 1. Put more test identifying details in the test name in test_fetching_by_id
 2. Change %id_tests to @id_tests so tests run in the order they are declared

From: http://blogs.perl.org/users/ovid/2014/03/perlqa-hackathon-in-lyon---summary.html#comment-1334582