Documentation for discovery and archiving plugins

[joemull]

Content needed

Librarian-facing documentation is needed for the set of plugins used for discovery and archiving:

• datacite - this one now has quite good docs
• doaj_transporter
• so_transporter
• ebsco_transporter
• portico
• loc_transporter
• lockss
• janeway-ftp

Context

There are two landing / overview pages so far:

• plugins/discovery-overview.md
• plugins/archiving-overview.md