Document shadow_copy module.

Document shadow_copy module.

NOTE - the formatting is a bit wonky because itemized list emits a
trailing .RE the messes up the indentation of the ssubsequent paragraph.
Also, itemizedlist emits character entities (dot points?) that man
doesn't appear to understand (ie. it renders them as  •).

suggestions welcome on how to fix the above :)
(This used to be commit 54b8f9b9c2e0cdd98471b52e3ef07c5f85276068)