Added google-groups to README
Added google-groups to README

Also removed completed backlog items
chafey/cornerstoneTools,google/cornerstoneTools,leonardorame/cornerstoneTools,swederik/cornerstoneTools,cornerstonejs/cornerstoneTools,cornerstonejs/cornerstoneTools,HorizonPlatform/cornerstoneTools,google/cornerstoneTools,swederik/cornerstoneTools,HorizonPlatform/cornerstoneTools,cornerstonejs/cornerstoneTools,leonardorame/cornerstoneTools