Fix sphinx error
[2022-01-17T16:03:27.448Z] /var/lib/jenkins/workspace/DSTO/tests-on-diff@2/docs/index.rst:25:hardcoded link 'https://archive.softwareheritage.org/api/' could be replaced by an extlink (try using ':swh_web:api/
' instead)
Migrated from D6960 (view on Phabricator)