Document `data-resources-url`

[thomasaull]

This is a follow up to https://github.com/ionic-team/stencil/issues/903. It seems like the attribute is still not documented (I can't find anything in the official docs at least). I figured it out by checking the generated source. I think this this might be helpful to others, so it should be documented.

Also I would question the practice to close issues which are inactive for a month even if the issue is not resolved yet. I know it's hard to stay on top of all those issues but by auto-closing (resolved or not) important things might get lost…

[splitinfinities]

Thank you for sharing this! I'm going to denote this as a part of our docs effort this quarter. Seems to fit quite well with assets too... I'll update you when it's ready, but it will be on the repo for the Stencil site, as a heads up.

[rwaskiewicz]

I'm gonna move this to the Stencil Site repo to make sure it gets grouped with similar issues, since we're looking to update the docs around the PR linked in the Issue Summary.