Add Arize Phoenix Python SDK Documentation

Description Request to add comprehensive documentation for the Arize Phoenix Python SDK.

What is Arize Phoenix? Open-source LLM observability platform with tracing, instrumentation, and evaluation capabilities.

Documentation Coverage

• Installation and setup
• Environment configuration
• Project registration and tracing
• Framework instrumentation (OpenAI, LangChain, CrewAI, Anthropic)
• Evaluation workflows
• Common mistakes section (prevents LLM hallucinations)
• Critical Phoenix vs Arize AX distinction

Links

• Official docs: https://arize.com/docs/phoenix
• GitHub: https://github.com/Arize-ai/phoenix