Add a minimal Sphinx docs build with reno release notes

.github/workflows/docs.yml

@@ -0,0 +1,69 @@
+name: Build Sphinx docs
+
+on:
+  workflow_dispatch:
+  push:
+    tags:
+      - "[0-9]+.[0-9]+.[0-9]+*"
+    branches:
+      - main
+      - 'stable/**'
+  pull_request:
+    branches:
+      - main
+      - 'stable/**'
+jobs:
+  build:
+    name: Build docs
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          # reno reads the tags and their history to assemble the release notes, and
+          # setup.py needs the vendored upstream headers to compile the extension.
+          fetch-depth: 0
+          submodules: recursive
+      - uses: actions/setup-python@v7
+        with:
+          python-version: '3.10'
+      - name: Install dependencies
+        # autodoc imports the package, so the extension has to compile here -- hence the
+        # same MPI and BLAS packages the test workflow installs, rather than the lighter
+        # set a pure-Python docs build would need.
+        run: |
+          python -m pip install --upgrade pip
+          pip install tox
+          sudo apt-get update
+          sudo apt-get install -y libopenmpi-dev openmpi-bin libopenblas-dev
+      - name: Build docs
+        shell: bash
+        # CPU only: the runner has no GPU toolchain, and the API reference does not
+        # depend on which backends were compiled.
+        env:
+          SBD_BUILD_BACKEND: cpu
+        run: |
+          tox -edocs
+      - name: Upload docs artifact
+        # Uploaded even on failure, which pairs with sphinx-build's --keep-going: the
+        # partial HTML is usually the fastest way to see what went wrong.
+        if: always()
+        uses: actions/upload-pages-artifact@v5
+        with:
+          path: docs/_build/html
+
+  deploy:
+    name: Deploy docs
+    if: ${{ github.ref == 'refs/heads/main' }}
+    needs: build
+    permissions:
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v5

.gitignore

@@ -10,6 +10,10 @@ build/
 dist/
 *.egg-info/
 
+# Sphinx documentation
+docs/_build/
+docs/stubs/
+
 # editor / OS noise
 .DS_Store
 *.swp