Deploy docs

Create basic documentation infrastructure for GitLab Pages.

Deploys a documentation page for cartolabe-data as https://hgozukan.gitlabpages.inria.fr/cartolabe-data/ to GitLab pages.

Later we can add API documentation. I would like to go over example notebooks and understand better the API and then we can decide what to expose.

Note: I've changed README.md to README.rst to be able to include it directly in documentation page.