Create docs landing page providing access to devel , sys-admin and user docs

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Migrated from T3867 (view on Phabricator)

mentioned in merge request !238 (closed)

marked this issue as related to #3649

added Documentation Roadmap 2022 meta-task priority:High labels

marked this issue as related to #3912

added priority:Normal label and removed priority:High label

marked this issue as related to #4496 (closed)

https://hedgedoc.softwareheritage.org/2022-11-17&18_docs-sprint-T5#

marked this issue as related to swh/meta#4844 (closed)

mentioned in merge request !267 (closed)

closed