docs: automate docs deployment on update (#196)

This adds a new workflow to GitHub Actions.

The action deploys an updated version of the documentation to GitHub
Pages.

It is triggered when changes are pushed to 'mkdocs.yaml' or anything
under the 'docs' folder on the 'main' branch.

This is necessary to make the docs up-to-date with our code, without
manual intervention.

Tested on my fork, although it required some tweaking there to adjust it
for testing purposes, so it might take some troubleshooting here in the
upstream.

Signed-off-by: Jacob Emery <jacob.emery@ibm.com>

.github/workflows/main.yaml

@@ -0,0 +1,31 @@
+name: Publish docs via GitHub Pages
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'mkdocs.yaml'
+      - 'docs/**'
+
+jobs:
+  build:
+    name: Deploy docs
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout main
+        uses: actions/checkout@v4
+        with:
+          ref: main
+
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.x'
+
+      - name: Install mkdocs
+        run: pip install mkdocs
+
+      - name: Deploy docs
+        run: python3 -m mkdocs gh-deploy
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}