[Feature Request]: Include the example in the documentation

### Feature description

In the example folder there is a extensive example of a joint model which would be a good addition to the documentation as a case study. The code could be copied and interlaced with explanatory text.

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct.

### Contribution Guidelines

- [X] I agree to follow this project's Contribution Guidelines.

### Security Policy

- [X] I agree to follow this project's Security Policy.

Start by reviewing the extensive joint-model example in the example folder and the repository's existing documentation structure. Turn the example into a case study by interlacing its code with explanatory text; done means the example is represented clearly and usefully in the documentation.

Written by the indexing model from the issue text.