Add root (`modules`) key to CONFIGURATION.md (#1009)

Add root (`modules`) key to CONFIGURATION.md (#1009)

* Add root (`modules`) key to CONFIGURATION.md

The Exporter configuration is complicated by the omission of the root (`modules`) key from the configuration document.

Not only must configuration begin with `modules` but each module is a map of module names to module values.

I think I've correctly reflected this here using the document's schema.

Signed-off-by: Daz Wilkin <DazWilkin@users.noreply.github.com>
* link to example.yml

Signed-off-by: Suraj Nath <9503187+electron0zero@users.noreply.github.com>
Signed-off-by: Daz Wilkin <DazWilkin@users.noreply.github.com>
Signed-off-by: Suraj Nath <9503187+electron0zero@users.noreply.github.com>
Co-authored-by: Suraj Nath <9503187+electron0zero@users.noreply.github.com>