Add checkout step to GitHub Actions workflow (#50)

The list of steps in the example for analyze-project skips repo checkout (which is required).

Updating this list makes it easier for users to just copy/paste the example usage.

Author: mshafer-NI

analyze-project/README.md

@@ -16,6 +16,8 @@ This action requires Poetry, so you must call `ni/python-actions/setup-python` a
 
 ```yaml
 steps:
+- name: Check out repo
+  uses: actions/checkout@v0
 - uses: ni/python-actions/setup-python@v0
 - uses: ni/python-actions/setup-poetry@v0
 - uses: ni/python-actions/analyze-project@v0