Add Continuous Integration support.

Make Github will automatically build any code  pushed to it.

.github/workflows/gradle.yml

@@ -0,0 +1,20 @@
+name: Java CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        submodules: 'recursive'
+    - name: Set up JDK 17
+      uses: actions/setup-java@v3
+      with:
+        distribution: 'temurin'
+        java-version: 17
+    - name: Build with Gradle
+      run: ./gradlew build