README: add TODO section with versions milestones
README: add TODO section with versions milestones

bORm/svgo,jagan-veeraraghavan/svgo,WebTwist/svgo,PeterWangPo/svgo,svg/svgo,ennett50/svgo,OrangeLV/svgo,subzey/svgo,ricardobeat/svgo,allypalanzi/svgo,pgherveou/svgo,ben-eb/svgo,pieter-lazzaro/svgo,akatopo/svgo,svg/svgo