Add a development section to the README

README.md

@@ -132,6 +132,25 @@ Granian is currently under active development.
 
 Granian is compatible with Python 3.8 and above versions.
 
+## Development
+
+You need installations of Rust and a recent Python 3 version.
+
+    # Set up a Python virtualenv
+    python3 -m venv .venv
+    source .venv/bin/activate
+    pip install -e .[test]
+
+    # Rebuild the Rust library if you change any Rust code
+    cargo build
+
+    # Run pytest
+    pytest
+
+    # You may optionally speed up the test suite by running tests in parallel
+    pip install pytest-xdist
+    pytest -n 16
+
 ## License
 
 Granian is released under the BSD License.