Resolve "specification" ✨️

Closes #6 🐔️👍️
Approved-by: aalbert <augustin.albert@bleu-azure.fr>
Approved-by: belazy <aarthuur01@gmail.com>
Approved-by: v-lafeychine <vincent.lafeychine@proton.me>

🦀️🍰🦀️🍰🦀️🍰

* docs: add specifications PDF

* docs: finish first version of the specifications

* docs: finish early description of specifications

* docs: add document template for specifiations

* feat(git): add LFS settings and TeX-specific .gitignore