add ToC to contrib guide
add ToC to contrib guide

Jinjiang/vue,posva/vue,greennyreborn/vue,posva/vue,sreesirisha/GITMidtermexam,wushuyi/vue,Kingwl/vue,KingMario/vue,xueyaodeai/vue,KingMario/vue,Jinjiang/vue,xueyaodeai/vue,cnchanning/vue,greennyreborn/vue,lizhiyao/vue,greennyreborn/vue,greennyreborn/vue,lizhiyao/vue,hanhongyuan/vue,Ddder-FE/vue,Hanks10100/vue,sreesirisha/GITMidtermexam,posva/vue,cnchanning/vue,cnchanning/vue,Hanks10100/vue,Ddder-FE/vue,Hanks10100/vue,leemotive/vue,vuejs/vue,KingMario/vue,pramudaprakash/GITHUB,Ddder-FE/vue,Kingwl/vue,pramudaprakash/GITHUB,pramudaprakash/GITHUB,gebilaoxiong/vue,hanhongyuan/vue,hanhongyuan/vue,gebilaoxiong/vue,KingMario/vue,lizhiyao/vue,leemotive/vue,Hanks10100/vue,pramudaprakash/GITHUB,sreesirisha/GITMidtermexam,Jinjiang/vue,gebilaoxiong/vue,vuejs/vue,Jinjiang/vue,vuejs/vue,leemotive/vue,leemotive/vue,Kingwl/vue,optimizely/vue,wushuyi/vue,xueyaodeai/vue,vuejs/vue,lizhiyao/vue,Kingwl/vue,hanhongyuan/vue,xueyaodeai/vue,sreesirisha/GITMidtermexam,posva/vue,Ddder-FE/vue