chore(docs): add example project (#59)

openai-java-example/build.gradle.kts

@@ -0,0 +1,18 @@
+plugins {
+    id("openai.kotlin")
+    id("java")
+    application
+}
+
+dependencies {
+    implementation(project(":openai-java"))
+}
+
+tasks.withType<JavaCompile>().configureEach {
+    // Allow using more modern APIs, like `List.of` and `Map.of`, in examples.
+    options.release.set(9)
+}
+
+application {
+    mainClass = "com.openai.example.Main"
+}