Unclear documentation about CA/cert files to pass with "repo add" on chartmuseum

In https://goharbor.io/docs/2.4.0/working-with-projects/working-with-images/managing-helm-charts/#add-harbor-to-the-repository-list , the `helm repo add` command-lines mention a parameter `--ca-file ca.crt`
But it's not explained where this ca.crt should be found?

The note below it says :

> Providing both a CA file and cert files is necessary due to an issue in Helm.

But the command-line only mentions one file, not two.

And it would be very helpful to give more detail on the corresponding Helm issue, and when it is needed (in my case, I did not seem to need it)