[SDKTECHNO-260] Rewrite the README files for app technologies (doc) v.2

[zannelo]

Additional context
Some of the apps in the Saagie repository require additional configuration to work. We have added a README file for these apps to help users install them. When installing an app, you can view its README file by clicking the [Read me] button on the card of the corresponding app. These files currently need to be reviewed and harmonized.

NOTE: This is a v.2 because of merge issues on the SDKTECHNO-259 PR.

[github-saagie]

Trello card: [#636] Rewrite the README files for app technologies (doc) v.2

[github-actions]

👍 JIRA Issue created : SDKTECHNO-260