Update index.md
Update index.md

Changing the date (adjusting to the SICSS Festival), specifying the application deadline (1 April 2022) and the topics covered (legal science).
compsocialscience/summer-institute,compsocialscience/summer-institute,compsocialscience/summer-institute,compsocialscience/summer-institute,compsocialscience/summer-institute,compsocialscience/summer-institute