Document usage of Poetry

README.md

@@ -1,8 +1,17 @@
 # Pillar Python REST SDK
 Integrate this module in your Python app to communicate with a Pillar server.
 
-Supports Python 3.5 and 3.6. Currently also supports Python 2.7, but support
-will be ending soon.
+Supports Python 3.5-3.7.
+
+
+## Development & Testing
+
+Dependencies are managed via [Poetry](https://poetry.eustace.io/).
+
+When starting development, run `poetry install` to create a virtual environment and install
+dependencies.
+
+To run the unit tests on all supported versions of Python, run `poetry run tox`.
 
 
 ## Caching