Include links to developer resources

[nemzes]

Currently a Google search for "responsive images" brings up responsiveimages.org near the top (2nd result on an incognito windows for me). That's great; but the chances are that someone searching for those terms are looking for information on how to use responsive images, not on the intricacies of the spec.

I suggest that the links under "Where can I learn more" are replaced with links to resources on how to use responsive images instead. There are plenty of great resources that have been mentioned on the newsletter. Here are a few suggestions:

• http://blog.cloudfour.com/responsive-images-101-definitions/
• http://www.danmatthew.co.uk/2015/04/19/implementing-responsive-images/
• https://scottjehl.github.io/picturefill/
• http://www.fivesimplesteps.com/products/practical-responsive-images

[marcoscaceres]

@nelsonmenezes any chance of PR?