Add workflow

.github/workflows/build.yml

@@ -0,0 +1,22 @@
+name: Build and upload mods
+
+on: push
+
+jobs:
+  packwizInstall:
+    runs-on: ubuntu-latest
+    container:
+      image: openjdk:21-jdk-alpine
+    steps:
+      - name: Install Node
+        run: apk add nodejs git
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Run Gradle jar
+        run: ./gradlew jar
+      - name: Upload mod artifact
+        if: success()
+        uses: actions/upload-artifact@v3
+        with:
+          name: mods
+          path: build/libs/*.jar