Adding the workflow to build the doxygen docs again

.github/workflows/doxygen.yml

@@ -0,0 +1,26 @@
+# Workflow that builds the doxygen documentation.
+
+name: Doxygen
+
+on:
+  push:
+    branches: [ master ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Doxygen Build
+        uses: mattnotmitt/[email protected]
+
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./doxygen/html/