Moving most of the inline docs in autorun.sh to scripts/README.md.
This makes the documentation more discoverable and approachable
(no need to read source code).
This commit also removes redundancies from the inline docs,
clears up some phrasing,
and uses more standard formatting and phrasing such as:
- using `` instead of ""
- calling itself `autorun.sh`
- calling pre and post "execution phases"