Rework the documentation

[tristanbes]

• On documentation index page, in 1/2 sentence, explain what does yProx-cli and what is its difference/advantages compared to other tools.
• On documentation index page, provide 1 simple example to have a global picture on how easy it is to use it.
• it minimize -> it minimizes
• Linting should have its own chapter in the documentation since it's a big "part" in term of features. Explain which tool it's using under the hood.
• Example -> Examples inside Environment variables and modes
• Rework this: https://github.com/Yproximite/yProx-cli/blob/master/README.md#L6

Thanks