Update user documentation of deposit

@douardda

I made a first deposit with no MD file, just a few options to the cli command (--author, --name and --slug) then I made a second deposit of the same zip file but with a metadata file (and no options) and I'm surprised by a few things:

1. the origin in the web app is https://softwareheritage.org/belenios-01234065 (belenios-0123456 being the slug I gave)
2. there is only one visit and revision the second deposit I made (with the metadata file) is not visible in the webapp (either as a visit nor another origin) nonetheless the deposit has been accepted (status: deposited)
3. I cannot see where I can find the metadata in the webapp (neither in the revision nor the directory view) (using a deposit instance in a freshly create docker dev stack) (you can try my webapp on http://192.168.101.170:5080 from the vpn)

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Migrated from T2740 (view on Phabricator)