Update README.md and CHANGELOG.md

1. Update README.md

2. In CHANGELOG.md : just refer to the gitlab public release notes = > https://gitlab.inria.fr/croco-ocean/croco_tools/-/releases

   => for v1.3 Think to update the v1.3 croco_tools release notes with the changelog section on the website

   => for v1.3 on the website, update : only refer to the gitlab release note

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