Updated test suite README

Hi folks,

In an effort to further encourage you (yes, you!) to write tests, I’ve
updated the repository readme in an attempt to make things clearer.

Comments (and pull requests with improvements!) most welcome.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh
Principal Engineer
MarkLogic Corporation
Phone: +1 512 761 6676
www.marklogic.com