Update/create documentation

[pschulzk]

The existing documentation is only provided in the GitHub repository's README.md and is insufficient.

An appropriate and extensive documentation about setting up, configuring and using the MeshUI is required.

• Language configuration
• Base URI configuration
• Keycloak configuraton (once supported)
• General introduction (Admin Area, Edit Area)
• Feature Overview (e.g. Bulk Upload )

[pschulzk]

@Jotschi recommends creating a docs folder and creating ASCII files within containing documentation.