ci: configure GitHub workflow

.github/workflows/gradle.yml

@@ -0,0 +1,27 @@
+name: Java CI with Gradle
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up JDK 17
+        uses: actions/setup-java@v3
+        with:
+          java-version: '17'
+          distribution: 'corretto'
+      - name: Build with Gradle
+        uses: gradle/gradle-build-action@3fbe033aaae657f011f88f29be9e65ed26bd29ef
+        with:
+          arguments: build

README.md

@@ -1,4 +1,6 @@
-# Activity Sampling
+![Java CI with Gradle](https://github.com/falkoschumann/activity-sampling-java/actions/workflows/gradle.yml/badge.svg)
+
+# Activity Sampling
 
 Periodically ask the user about their current activity and log it for analysis.