docs(ci): Add workflow to build and deploy docs

Separate workflows for `push` and `pull_request` events. This avoids a `skipped` job status (`Check Run`?) always being presented for the `deploy` job in Pull Requests.

---

chore(`.gitignore`): Ignore the `docs/site/` build output

Ignore to avoid local builds output appearing in git as unstaged.

.github/workflows/deploy-docs.yml

@@ -0,0 +1,33 @@
+name: 'Documentation'
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - master
+    paths:
+      - '.github/workflows/deploy-docs.yml'
+      - 'docs/**'
+
+# Jobs will run shell commands from this subdirectory:
+defaults:
+  run:
+    working-directory: docs
+
+jobs:
+  deploy:
+    name: 'Deploy Docs'
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: 'Build with mkdocs-material via Docker'
+        run: docker run --rm -v ${PWD}:/docs squidfunk/mkdocs-material build --strict
+
+      - name: 'Deploy to Github Pages'
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./docs/site
+          user_name: 'github-actions[bot]'
+          user_email: '41898282+github-actions[bot]@users.noreply.github.com'

.github/workflows/pr-docs.yml

@@ -0,0 +1,22 @@
+name: 'Documentation'
+
+on:
+  pull_request:
+    paths:
+      - '.github/workflows/pr-docs.yml'
+      - 'docs/**'
+
+# Jobs will run shell commands from this subdirectory:
+defaults:
+  run:
+    working-directory: docs
+
+jobs:
+  build:
+    name: 'Verify Build'
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: 'Build with mkdocs-material via Docker'
+        run: docker run --rm -v ${PWD}:/docs squidfunk/mkdocs-material build --strict

.gitignore

@@ -46,3 +46,5 @@ test/duplicate_configs
 
 config.bak
 testconfig.bak
+
+docs/site