Really? I started playing around with and it not clear how to do this with helm.
Sorry for the confusion!
To use a URL, I think you'd either have to push up the packaged chart as a .gzip file in your repo (which is annoying), or you'd have to package up the chart and create a GitHub release with the resulting gzip file to be able to reference it that way. In GitLab you might be able to point to a pipeline artifact[0] after packaging the chart using GitLab CI.
In one experimental project[1], I'm using GitLab Pages to package and publish the index. It works out surprisingly well, but has some shortcomings.
[0]: https://docs.gitlab.com/ce/user/project/pipelines/job_artifa... [1]: https://gitlab.com/charts/charts.gitlab.io