user docs:: write content for "Getting to know the archive" section

Getting to know the Software Heritage archive

Add direct link to the Guided tour + video of the guided tour

Tutorial: Searching an origin

Tutorial: Browsing the universal source code archive

How to get and choose a swhid in the archive

How to list visits

How to submit a save code now request

How to download content

How to use the API

existing scripts examples

Reference: pull vs push - overview of the Software Heritage archival strategy

Lister and loader

Deposit on a partner's platfrom

Reference: Archive, Reference, Describe and Cite source code using Software Heritage

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Migrated from T4245 (view on Phabricator)