Update to Informational Graphic Contrast (Minimum)

I have added 7. EM Proposed Description for review:

https://www.w3.org/WAI/GL/low-vision-a11y-tf/wiki/Informational_Graphic_Contrast_%28Minimum%29#EM_Proposed_Description

Thank you,
                                                                                       
                    Erich Manser                                                       
                    IBM                                                                
                    Accessibility,                                                     
                    IBM Research                                                       
                    Littleton,                                                         
                    MA / tel:                                                          
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You don't need eyesight to have vision.