Document the user support on the website

Document the existence of the list and the twin #swh channel on the website :

create a https://www.softwareheritage.org/community/users/ analogous to https://www.softwareheritage.org/community/developers/ , listing two "resources", the chat channel and the mailing list
mention this page in the https://www.softwareheritage.org/faq/ page
- mention page in WIP FAQ: https://hedgedoc.softwareheritage.org/lw-XTHaYQv2fDPJ9bIpU1Q?both

Migrated from T4323 (view on Phabricator)

Edited Jan 08, 2023 by Phabricator Migration user

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