Add docs

Author: Danny McCormick

README.md

@@ -1,3 +1,45 @@
 # setup-python
 
-This action sets the python environment for use in actions
+This action sets up a python environment for use in actions by:
+
+- optionally downloading and caching a version of python by version and adding to PATH
+- registering problem matchers for error output
+
+# Usage
+
+See [action.yml](action.yml)
+
+Basic:
+```yaml
+actions:
+- uses: actions/setup-python@latest
+  with:
+    version: 3.x // Version range or exact version of a Python version to use, using semvers version range syntax.
+    architecture: x64 // (x64 or x86)
+- run: python my_script.py
+```
+
+Matrix Testing:
+```yaml
+jobs:
+  build:
+    strategy:
+      matrix:
+        python: [ 2.x, 3.x, pypy3 ]
+    name: Python ${{ matrix.python }} sample
+    actions:
+      - name: Setup python
+        uses: actions/setup-python@latest
+        with:
+          version: ${{ matrix.python }}
+          architecture: x64
+      - run: python my_script.py
+```
+
+# License
+
+The scripts and documentation in this project are released under the [MIT License](LICENSE)
+
+# Contributions
+
+Contributions are welcome!  See [Contributor's Guide](docs/contributors.md)