Update README with missing Pixi support, fix typo, and add comprehensive build instructions

[Copilot]

This PR updates the README to reflect the current state of the Python Environment Tools project and improve documentation for users and contributors.

Changes Made

Fixed Missing Environment Type

• Added Pixi to the supported environment types list, which was missing despite being fully implemented in the codebase via the pet-pixi crate
• Updated the environment type count from "15+" to "17+" to accurately reflect the current supported types

Fixed Typo

• Corrected "JSNORPC" to "JSONRPC" in the project description

Enhanced Documentation

• Added comprehensive Build and Usage section with practical examples:

  • Step-by-step build instructions using cargo
  • CLI usage examples for all three main commands (server, find, resolve)
  • Links to detailed JSONRPC API documentation

• Expanded Features section to better highlight the project's capabilities:

  • Added performance benefits using Rust
  • Mentioned JSONRPC server interface for IDE integration
  • Updated platform support information

• Enhanced Key Methodology section with detailed Performance Principles:

  • Avoid spawning processes
  • Report immediately using asynchronous discovery
  • Complete information gathering in one pass
  • Minimal I/O operations

Verification

• All changes maintain backward compatibility
• Build and tests continue to pass
• CLI commands mentioned in the README work correctly
• Security checks (CodeQL) and linting (cargo fmt, clippy) pass without issues

These updates make the README more accurate, comprehensive, and useful for both users wanting to understand the project's capabilities and developers looking to build and contribute to the codebase.

Created from VS Code via the GitHub Pull Request extension.

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