The github.io site that they include the link to is the actual repository that can be read by Helm, in particular by it polling the known "index.yaml" file at https://teslamotors.github.io/helm-charts/index.yaml. Something _could_ be done using Github's "/raw" endpoint, but generally speaking Github pages works better for this sort of purpose and also is built to be a CDN, meaning it has additional caching layers in front of it that make it more performant.