Fix jupyterlite config to include content by default

• Bump jupyterlite version to 1.2 and update dependencies
• Update README description to create a new JupyterLite and badge
• Update jupyterlite configuartion (to include favicon)
• Add example notebook in files/ folder

requirements.txt

-jupyterlite>=0.1.2
-jupyterlab_server
+# Core modules (mandatory)
+jupyterlite-core>=0.1.2
+jupyterlab~=3.5.1
+
+# Language support (optional)
 jupyterlab-language-pack-fr-FR
+
+# Python kernel (optional)
+jupyterlite-pyodide-kernel==0.1.1
+
+# Local speed-up compiler
+libarchive-c
+
+
+# Notebook dependencies
+numpy
+matplotlib