workflows: docs: add

Create a custom workflow for deploying our documentation to GitHub
Pages. This allows us to retain the original YAML-to-documentation
generation process we've used in the past, and stops us from relying
solely on files already being on the main branch for documentation build
and review.

We have to incorporate two new community actions for this:

1. `peaceiris/actions-gh-pages`, for deploying the actual docs using a
   `gh-pages` branch
2. `rossjrew/pr-preview-action`, for creating docs previews so we're
   able to review the changes before merge. Comments will be posted on
   the PR providing preview links.

AI-Generated: Uses Claude Sonnet 5

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc

.github/workflows/docs.yml

@@ -0,0 +1,108 @@
+# SPDX-FileCopyrightText: 2026 The RISE Project
+# SPDX-License-Identifier: MIT
+
+name: Build and deploy documentation
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "docs/**"
+  pull_request:
+    types: [opened, synchronize, reopened, closed]
+  workflow_dispatch:
+
+concurrency:
+  group: docs-${{ github.ref }}
+
+jobs:
+  preview:
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        if: github.event.action != 'closed'
+        with:
+          python-version: '3'
+
+      - name: Install package doc generator dependencies
+        if: github.event.action != 'closed'
+        run: pip install -r docs/requirements.txt
+
+      - name: Generate package pages from YAML
+        if: github.event.action != 'closed'
+        run: python docs/packages/generate_packages_doc.py
+
+      - name: Compute preview baseurl
+        if: github.event.action != 'closed'
+        id: preview_baseurl
+        run: |
+          base=$(python3 -c "import yaml; print(yaml.safe_load(open('docs/_config.yml'))['baseurl'])")
+          echo "value=${base}/pr-preview/pr-${{ github.event.number }}" >> "$GITHUB_OUTPUT"
+
+      - uses: ruby/setup-ruby@v1
+        if: github.event.action != 'closed'
+        with:
+          ruby-version: '3.3'
+
+      # actions/jekyll-build-pages has no way to override _config.yml's
+      # hardcoded baseurl, but a preview is served one path segment deeper
+      # (.../pr-preview/pr-<N>/) than the production site, so it needs its
+      # own baseurl or every internal link/asset would point at production.
+      - name: Build with Jekyll
+        if: github.event.action != 'closed'
+        run: |
+          # jekyll-remote-theme only fetches just-the-docs' layouts/assets;
+          # its own gem dependencies (jekyll-seo-tag, jekyll-include-cache,
+          # rake) still have to be installed separately.
+          gem install jekyll jekyll-remote-theme jekyll-seo-tag jekyll-include-cache rake --no-document
+          jekyll build --source docs --destination _site \
+            --baseurl "${{ steps.preview_baseurl.outputs.value }}"
+
+      # Auto-detects deploy vs. removal from the pull_request event action,
+      # so this same step both publishes updates and tears down the preview
+      # when the PR is closed. wait-for-pages-deployment blocks until Pages
+      # has actually rebuilt with the new content before posting the PR
+      # comment/link, otherwise the link 404s for whatever GitHub Pages'
+      # build lag happens to be.
+      - name: Deploy or remove PR preview
+        uses: rossjrw/pr-preview-action@v1
+        with:
+          source-dir: ./_site
+          wait-for-pages-deployment: true
+
+  deploy:
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3'
+
+      - name: Install package doc generator dependencies
+        run: pip install -r docs/requirements.txt
+
+      - name: Generate package pages from YAML
+        run: python docs/packages/generate_packages_doc.py
+
+      - name: Build with Jekyll
+        uses: actions/jekyll-build-pages@v1
+        with:
+          source: ./docs
+          destination: ./_site
+
+      - name: Deploy to GitHub Pages
+        uses: peaceiris/actions-gh-pages@v4
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./_site
+          keep_files: true