Add dependency information.

README.md

@@ -30,3 +30,21 @@ make documentation
 ```
 
 Documentation will end up in `doc.rendered/`.
+
+
+Dependencies
+------------
+
+General python dependencies are documented in [./setup.cfg](`setup.cfg`).
+
+### Runtime dependencies
+- Puppet
+- Puppet Strings
+
+### Testing dependencies
+- `flake8`
+- `mypy`
+- `pytest`
+
+### Documentation dependencies
+- sphinx