Replace BUILD.md with CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing
+
+## Setup
+
+Requires Python 3.10 or later.
+
+```sh
+pip install -e . --group dev
+```
+
+## Running Tests
+
+```sh
+pytest
+
+# With coverage:
+pytest --cov=instaparser
+```
+
+## Linting & Type Checking
+
+```sh
+ruff check instaparser/ tests/
+ruff format --check instaparser/ tests/
+mypy
+```
+
+## Versioning
+
+The package version is defined in `instaparser/__init__.py` and read by setuptools at build time via `[tool.setuptools.dynamic]` in `pyproject.toml`.