[Docs] Add user docuentation

[erwanschild]

Is your feature request related to a problem? Please describe.

There is a technical documentation, but a user documentation is missing. It lacks of:

• app advertising,
• user understanding,
• feature description.

Describe the solution you'd like

• add screenshots,
• add description of interactive clustering steps and features,
• add dummy dataset to test easily.

Additional context

This documentation should be in:

• README.md,
• app documentation
• app welcome page.