FTP importer docs / general transporter docs

[S-Haime]

Content needed

We currently only have:
https://github.com/openlibhums/memory-alpha/blob/b-support-site-mvp/content/pages/support/plugins/production-transporter.md
https://github.com/openlibhums/memory-alpha/blob/b-support-site-mvp/content/pages/support/plugins/discovery-overview.md

Having more than this would be good. Some basic overviews of what they are and can/can't do would be good starts.

If this will sit in dev docs, let me know. I will then update the users docs accordingly.