Auto-generate index.html

[doug-wade]

Is your feature request related to a problem? Please describe.
I often edit my digital garden via the web interface on GitHub. Adding a new file, or editing an existing file is very easy, but I consistently forget to add the new note to my index.html.

Describe the solution you'd like
I would like to auto-generate an index.html that contains a link to every note. Not every user might want this behavior, so I would also like a way to opt in or out of this feature.

Describe alternatives you've considered
I have considered being more rememberful, but I have not been very successful heretofore, and I don't think it's gonna happen.

Additional context
We probably need the ability to specify a template for the generated page.

We can probably generate other files (a sitemap, a manifest.json, etc) during the same pass over the filesystem.

[doug-wade]

I really like this template and have used it a lot, so if this is a feature we want, I'd be interested in implementing it.