Add a component documentation

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Including:

• [ ] Props & Methods (update : maybe have a look at https://github.com/reactjs/react-docgen which seems used by Styleguidist and Storybook)
• [x] Example
• [ ] All versions

[slafayIGN]

Example of Card Style here : https://geostyler.github.io/geostyler-docusaurus/docs/components/card-style/

With a second sidebar dedicated to the components (the first one being for tutorials)