Add a small documentation for ApprovalTests

src/main/resources/generator/server/javatool/approvaltesting/aprroval-testing.md

@@ -0,0 +1,26 @@
+# Approval based testing with ApprovalTests
+
+Instead of writing individual assertions, ApprovalTests focuses on verifying the overall output. This is particularly useful when testing complex objects, files, or outputs where writing assertions would be tedious.
+
+Here is the example of approval-based tests from [ApprovalTests.java User Guide](https://github.com/approvals/ApprovalTests.Java/blob/master/README.md)
+
+```java
+import java.util.Arrays;
+import org.approvaltests.Approvals;
+import org.junit.jupiter.api.Test;
+
+public class SampleArrayTest {
+
+  @Test
+  public void testList() {
+    String[] names = { "Llewellyn", "James", "Dan", "Jason", "Katrina" };
+    Arrays.sort(names);
+    Approvals.verifyAll("", names);
+  }
+}
+
+```
+
+This will a File `SampleArrayTest.testList.received.txt`
+
+Simply rename this to `SampleTest.testList.approved.txt` and the test will now pass.