Simplify and modernize README with clearer structure

[alexkroman]

Restructures the README to be more scannable and user-focused, replacing the centered HTML layout with a cleaner markdown format that emphasizes key features and getting started quickly.

Changes

• Simplified header: Replaced centered HTML/link wrapper with a plain markdown heading and inline badges for Python version, license, and docs
• Reorganized content flow:
  • Added "Why the AssemblyAI CLI?" section highlighting core value propositions (pipeline-friendly, secure by default, agent-ready, etc.)
  • Moved installation instructions earlier and condensed Homebrew description
  • Consolidated feature descriptions into a "Key Features" section with command-to-capability mapping
  • Separated authentication into its own section with clear Option 1 (browser login) and Option 2 (env var) paths
• Streamlined getting started: Added "Getting Started" section with basic usage examples and quick examples showing common patterns
• Reduced verbosity:
  • Removed detailed explanations of exit codes, JSON shapes, and telemetry (moved to docs)
  • Condensed account self-service and AI coding agents sections
  • Removed the lengthy "Pipelines" section in favor of concise examples
  • Simplified development section to point to AGENTS.md for conventions
• Improved scannability: Used emoji headers and bullet points to break up dense text blocks

The README now prioritizes getting users to their first command quickly while maintaining links to detailed documentation for advanced topics.

https://claude.ai/code/session_01Bmbyb8SgCwc9vjPoju6b7y