Update README.md with comprehensive user documentation

[bergsalex]

NOTE: This PR was created by an LLM agent.

^*-~ 🤖 beep boop ~~*^

This PR improves the README.md to make JABS-postprocess more accessible to new users.

• Restructured installation guide with PyPI as the recommended approach, including uv, pip, Docker, and Singularity options
• Added comprehensive usage examples covering three main workflows:
  • Basic behavior table generation
  • Heuristic classification workflow
  • Video snippet creation with overlays
• Explained key concepts (bouts, filtering parameters, data organization) with clear examples
• Added troubleshooting section addressing 7 common issues with actionable solutions
• Included working code examples for data analysis and visualization
• Added links to configuration files and example scripts
• Organized content for better readability and progressive disclosure

The documentation now provides a complete pathway from installation through advanced usage, making it easier for researchers to adopt and effectively use JABS-postprocess for behavioral analysis.