.github/workflows/pages.yml: add comments

.github/workflows/pages.yml

@@ -12,6 +12,9 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
+          # 2021-12-14 this is currently an OK choice, but it will need to be
+          # updated eventually as the ecosystem moves. Keep in sync with the
+          # version in pyproject.toml.
           python-version: 3.9
       - name: Install Poetry
         uses: abatilo/actions-poetry@v2.1.4
@@ -29,6 +32,7 @@ jobs:
         uses: stefanzweifel/git-auto-commit-action@v4
         with:
           commit_message: Automated commit with site updates
+          # Only commit if there are changes to the site.
           file_pattern: site/*
   pages:
     runs-on: ubuntu-latest