Add Github Workflow to publish on Pages

The workflow is lightly adapted from the one suggested in theSphinx
documentation [1].
It builds and pushes the website to the "gh-pages" branch which can then
be published from the repository's settings [2].
A push event to "master" triggers the workflow. [3]

[1] https://www.sphinx-doc.org/en/master/tutorial/deploying.html#id5
[2] https://docs.github.com/en/pages/getting-started-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site#publishing-from-a-branch
[3] https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#push

Author: Louis Nicolas Stenger

.github/workflows/sphinx.yml

@@ -0,0 +1,32 @@
+name: "Sphinx: Build Fortran90.org"
+
+on:
+  push:
+    branches:
+      - "master"
+
+
+permissions:
+  contents: write
+  id-token: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build HTML
+      uses: ammaraskar/sphinx-action@master
+      with:
+        docs-folder: "./"
+    - name: Upload artifacts
+      uses: actions/upload-artifact@v4
+      with:
+        name: html-docs
+        path: _build/html/
+    - name: Deploy
+      uses: peaceiris/actions-gh-pages@v4
+      if: github.ref == 'refs/heads/master'
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        publish_dir: _build/html