Add CLAUDE.md with project structure and commands

Author: Kludex

CLAUDE.md

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+# OpenTelemetry Python Contrib
+
+Monorepo with 50+ OpenTelemetry instrumentation packages for Python.
+
+## Structure
+
+- `instrumentation/` - instrumentation packages (Flask, Django, FastAPI, gRPC, databases, etc.)
+- `instrumentation-genai/` - GenAI instrumentations (Anthropic, Vertex AI, LangChain, etc.)
+- `util/` - shared utilities (`util-http`, `util-genai`)
+- `exporter/` - custom exporters
+- `propagator/` - context propagators
+
+Each package lives under `src/opentelemetry/instrumentation/{name}/` with its own `pyproject.toml` and `tests/`.
+
+## Commands
+
+```sh
+# Install all packages and dev tools
+uv sync --frozen --all-packages
+
+# Lint (runs ruff via pre-commit)
+uv run pre-commit run ruff --all-files
+
+# Test a specific package (append -0, -1, etc. for version variants)
+uv run tox -e py312-test-instrumentation-flask-0
+
+# Type check
+uv run tox -e typecheck
+```
+
+## Guidelines
+
+- Each package has its own `pyproject.toml` with version, dependencies, and entry points.
+- The monorepo uses `uv` workspaces.
+- `tox.ini` defines the test matrix - check it for available test environments.
+- Do not add `type: ignore` comments. If a type error arises, solve it properly or write a follow-up plan to address it in another PR.