feat: setup gradle pour lancer l'app et les test, ajout des commandes dans le README.md

app/src/main/java/sudoku/App.java

@@ -0,0 +1,14 @@
+/*
+ * This Java source file was generated by the Gradle 'init' task.
+ */
+package sudoku;
+
+public class App {
+    public String getGreeting() {
+        return "Hello World!";
+    }
+
+    public static void main(String[] args) {
+        System.out.println(new App().getGreeting());
+    }
+}