Improve country module documentation
Documentation improvements as part of the GSoD: https://discuss.tryton.org/t/gsod-project-documentation-for-basic-modules/3186
This instance will be upgraded to Heptapod 1.5.0rc (GitLab 16.11.1) on 2024-05-02 at 15:00 UTC+2
Documentation improvements as part of the GSoD: https://discuss.tryton.org/t/gsod-project-documentation-for-basic-modules/3186