.github/workflows/build.yml: new GitHub Action

.github/workflows/build.yml

@@ -0,0 +1,33 @@
+name: Build Bisq
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-18.04
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+        ref: ${{ github.event.pull_request.head.sha }}
+        lfs: true
+
+    - name: Set up JDK
+      uses: actions/setup-java@v2
+      with:
+        java-version: '11'
+        distribution: 'adopt'
+
+    - name: Grant execute permission for gradlew
+      run: chmod +x gradlew
+
+    - name: Validate Gradle Wrapper JAR files
+      uses: gradle/wrapper-validation-action@v1
+
+    - name: Build with Gradle
+      run: ./gradlew build