fix: add example src and tests

Signed-off-by: Charlike Mike Reagent <opensource@tunnckocore.com>

Author: tunnckoCore

src/__tests__/index.js

@@ -0,0 +1,5 @@
+import mod from '..';
+
+test('example test', () => {
+  expect(typeof mod).toStrictEqual('function');
+});

src/index.js

@@ -0,0 +1,9 @@
+/**
+ * Program main entry point.
+ */
+export default () => {};
+
+/**
+ * When CLI interface is needed.
+ */
+export const cli = () => {};