Change text "Click me" to somthing else (#4697)

The Text "Click me" in the button confuses first-time users because it forces them to actually click on the button in the live demo but it does nothing. By changing the text, we can control the user behavior as they don't expect anything on that click.

beta/src/pages/learn/index.md

@@ -28,7 +28,7 @@ React components are JavaScript functions that return markup:
 ```js
 function MyButton() {
   return (
-    <button>Click me</button>
+    <button>I'm a button</button>
   );
 }
 ```
@@ -56,7 +56,7 @@ Have a look at the result:
 function MyButton() {
   return (
     <button>
-      Click me
+      I'm a button
     </button>
   );
 }