Add building the docs

Needed Java/gradle and to actually create the things

.github/workflows/jekyll-gh-pages.yml

@@ -28,6 +28,17 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+      # get java
+      - name: Java
+        uses: actions/setup-java@v3
+        with:
+          java-version: '17'
+          distribution: "temurin"
+      # build docs
+      - name: Build docs
+        run: |
+          cd docs
+          ./gradlew --no-daemon --quiet clean dokkaJavadoc        
       - name: Setup Pages
         uses: actions/configure-pages@v4
       - name: Build with Jekyll