Update transform-es2015 READMEs from babel.github.io [skip ci] (#4926)

Signed-off-by: Brian Ng <bng412@gmail.com>

packages/babel-plugin-transform-es2015-modules-amd/README.md

@@ -1,5 +1,29 @@
 # babel-plugin-transform-es2015-modules-amd
 
+> This plugin transforms ES2015 modules to [Asynchronous Module Definition (AMD)](https://github.com/amdjs/amdjs-api).
+
+## Example
+
+**In**
+
+```javascript
+export default 42;
+```
+
+**Out**
+
+```javascript
+define(["exports"], function (exports) {
+  "use strict";
+
+  Object.defineProperty(exports, "__esModule", {
+    value: true
+  });
+
+  exports.default = 42;
+});
+```
+
 ## Installation
 
 ```sh