chore: added documentation to GitHub action

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.9.9'
+          python-version: '3.9.9' # no particular microversion of 3.9 is required; 3.9.8 behaves oddly in GitHub actions
 
       - name: Setup pip cache
         uses: actions/cache@v2