docs: Fix sphinx warning
the tutorial.md
suggestion change was fishy and not working [1]
17:21:21 /var/lib/jenkins/workspace/DDOC/build-on-diff/swh-docs/docs/swh-fuse/tutorial.md:85: WARNING: hardcoded link 'https://archive.softwareheritage.org/api/' could be replaced by an extlink (try using ':swh_web:`api/`' instead)
So the tutorial got converted into markdown to nail it.
Related to swh-docs!294 (closed)
Test Plan
make -C docs
happy now
Migrated from D6970 (view on Phabricator)