Simplify doc build workflow and expand requirements

.github/workflows/build_docs.yaml

@@ -5,12 +5,7 @@ on:
       - docs
 jobs:
   build-docs:
-    runs-on: ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest]
-        python-version: ['3.10']
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
       - name: Set up Python ${{ matrix.python-version }}
@@ -21,7 +16,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y pandoc
-          python -m pip install sphinx sphinx_design sphinx-rtd-theme sphinxcontrib-bibtex
+          python -m pip install sphinx sphinx_design sphinx-rtd-theme sphinxcontrib-bibtex numpydoc
       - name: Build docs
         run: cd doc && make html
       - name: Deploy to GitHub Pages