Autoreload docs page

When running `ember serve --docs` I thought the docs page would have an auto-reload which it didn't. Would be a timesaver to have it.

Start by reproducing the behavior with `ember serve --docs` and observe how documentation changes are served. Trace the docs-serving entry point and determine where a reload would be integrated; the work is done when changing documentation while the command runs automatically refreshes the docs page.

Written by the indexing model from the issue text.