Motivation

• Clarify how the vpython wrapper works and document common usage patterns for new users.
• Explain dependency installation modes and how the wrapper decides when to (re)install dependencies.
• Surface the available environment knobs (e.g. PYWRAP_BASE_PYTHON, PYWRAP_VENV_MODE) for configuration.
• Document concurrency and venv self-healing behavior to reduce surprises during concurrent runs.

Description

• Expanded README.md with a How it works section that outlines the runtime flow used by the wrapper.
• Added a Usage section with example invocations such as ./python3 -c "print('hello from vpython')" and ./python3 -m pip --version.
• Added Dependency installation modes and Environment variables sections describing requirements, pyproject, and none modes and the available PYWRAP_* settings.
• Added Notes describing the cross-platform file lock behavior and the wrapper's venv self-heal logic and metadata file location (.venv/.pywrap/ok.json).

Testing

• No automated tests were run because this is a documentation-only change.
• Repository unit tests were not executed as part of this update.
• Linting or CI was not invoked for this commit.
• The change only modifies README.md and does not affect runtime code paths.

Codex Task