Resolve "Preparations for the first release" ✨️

Closes #48 🐔️👍️
Approved-by: aalbert <augustin.albert@bleu-azure.fr>
Approved-by: v-lafeychine <vincent.lafeychine@proton.me>

🦀️🍰🦀️🍰🦀️🍰

* chore: change branch name mentions to main

* feat(docs): add user manual

* fix(rustyline): autocompletion format: bold -> grey

* doc(all): add Proost logo

* doc(rustyline_helper): minor URL adjustments

* chore(README): update

* feat(README): add Proost logo

* feat(docs): add Proost logo in specification (LFS test in disguise)