Primer contribution on "Enabling easy message dispatching" - Done

Hi Umit,

Thanks for the contribution. I have added some lead text in [1], and
replacing the text [2] in with your contribution with some minor
editing. 

[1]
http://dev.w3.org/cvsweb/~checkout~/2002/ws/desc/wsdl20/wsdl20-primer.ht
ml#N67927
[2]
http://dev.w3.org/cvsweb/~checkout~/2002/ws/desc/wsdl20/wsdl20-primer.ht
ml#adv-message-dispatch

Please check it out and let me know you are not satisfied with my
editings.

Best Regards,
Kevin