Add a link to chartjs-plugin-rough to extensions.md (#6081)
Add a link to chartjs-plugin-rough to extensions.md (#6081)


touletan/Chart.js,nnnick/Chart.js,chartjs/Chart.js,touletan/Chart.js,touletan/Chart.js,chartjs/Chart.js,chartjs/Chart.js,touletan/Chart.js,chartjs/Chart.js