Add back docs/requirements.txt

Add conditional installation of documentation requirements.

Author: olivialynn

python-project-template/.github/workflows/{% if include_docs %}build-documentation.yml{% endif %}.jinja

@@ -31,6 +31,7 @@ jobs:
       run: |
         sudo apt-get update
         uv pip install --system -e .
+        if [ -f docs/requirements.txt ]; then uv pip install -r docs/requirements.txt; fi
         if [ -f requirements.txt ]; then uv pip install --system -r requirements.txt; fi
 {%- if include_notebooks %}
     - name: Install notebook requirements