Add real-world examples and JSON/NDJSON input docs to README

[vmvarela]

The README only documents CSV input and lacks concrete real-world examples.

Changes needed

• Update intro and Usage section to cover JSON and NDJSON input (-I json, -I ndjson)
• Add -I/--input-format and -O/--output-format to the flags table
• Fix the existing chain example (missing -H on first call)
• Add a Real-world examples section with 6 verified live examples:
  • La Liga all-time home wins (CSV)
  • La Liga highest-scoring seasons with --json output (CSV)
  • OWID energy: top solar countries 2023 (CSV)
  • OWID energy: wind + solar two-pass chain (CSV + chaining)
  • restcountries Europe population density (NDJSON + jq)
  • Open-Meteo 7-day Madrid forecast (NDJSON + jq)