Add docs of pagination context with context modifiers

[thibaudcolas]

This is more docs and demo for #141, following #147.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• [ ] I have added an appropriate CHANGELOG entry