Add visual examples

### Describe the change you would like to see:
Add more visual examples to show input behavior and use cases

### How would the suggested change make the documentation more useful?
More easy to understand the input

### Additional context:
Related to https://github.com/flutter-form-builder-ecosystem/flutter_form_builder/issues/1027

Start by reviewing the repository's existing documentation and examples to find where input behavior and use cases are currently shown. Add visual examples covering those areas, with completion marked by clearer documentation that demonstrates the requested input behavior and use cases.

Written by the indexing model from the issue text.