docs(repo_faq): create chart_repository_faq.md

Add FAQ for `unsupported protocol scheme ""` error

docs/chart_repository_faq.md

+# Chart Repositories: Frequently Asked Questions
+
+This section tracks some of the more frequently encountered issues with using chart repositories.
+
+**We'd love your help** making this document better. To add, correct, or remove
+information, [file an issue](https://github.com/kubernetes/helm/issues) or
+send us a pull request.
+
+## Fetching
+
+**Q: Why do I get a `unsupported protocol scheme ""` error when trying to fetch a chart from my custom repo?**
+
+A: This is likely caused by you creating your chart repo index without specifying the `--url` flag.
+Try recreating your `index.yaml` file with a command like `heml repo index --url http://my-repo/charts .`,
+and then re-uploading it to your custom charts repo.