Add a "Tutorial" link at the top of api pages

• https://archive.softwareheritage.org/api/
• https://archive.softwareheritage.org/api/1/

To link to https://docs.softwareheritage.org/devel/getting-started/api.html new location should be: https://docs.softwareheritage.org/user/getting-started/api.html or https://docs.softwareheritage.org/user/tutorial/api.html

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Migrated from T3913 (view on Phabricator)