docs: also publish docs to github pages (#1955)

* docs: also publish docs to github pages

So just in case people can't access the Cloudflare Pages docs,
they can still access the GitHub ones.

* temporarily add to PR as trigger to test

* ok

.github/workflows/publish_github_pages.yml

@@ -0,0 +1,44 @@
+# Workflow to publish to GitHub Pages. Based on the normal
+# job (e.g. https://github.com/ClementTsang/bottom/actions/runs/19805277892),
+# but re-implemented so I can pin hashes.
+#
+# This action uses actions/upload-pages-artifact, which uses actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 (v4.6.2).
+
+name: Publish GitHub Pages
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - gh-pages
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+        with:
+          ref: gh-pages
+          submodules: recursive
+          fetch-depth: 1
+
+      - name: Upload artifact
+        id: upload
+        uses: actions/upload-pages-artifact@7b1f4a764d45c48632c6b24a0339c27f5614fb0b # v4.0.0
+        with:
+          path: "./"
+
+  deploy:
+    runs-on: ubuntu-latest
+    needs: build
+    environment:
+      name: github-pages
+      url: ${{ steps.deploy.outputs.page_url }}
+    permissions:
+      pages: write
+      id-token: write
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deploy
+        uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e # v4.0.5