Status of the repo for Simple Lit

[Zallist]

Looks to be all completed to the exact same standards as Unity itself.
No new features will be added to this now, unless they're also added to the Lit/Unlit master nodes. Only bug fixes.

If URP version 14/15/16 breaks this and an issue hasn't been raised already, raise one. Hopefully Unity will adopt this properly before they have a chance to break it, though.