Update Readme with the latest infos

This chart is very useful so i updated it. Safari 6.1 now supports -webkit-clip-path with basic shapes on HTML content and -webkit-filter. But i haven't test if clip-path is supported on SVG content. Firefox supports clip-path with SVG on HTML content.

Let me know if you find something wrong.

Vincent
Merged iamvdo-patch-1
Merge branch 'iamvdo-patch-1'