adding demo code from variables module

Author: aaronpowell

05-variables/demo.js

@@ -0,0 +1,16 @@
+var hello = "Hello";
+
+console.log(hello);
+hello = "Hello World";
+console.log(hello);
+
+if (true) {
+    let world = "Hello World";
+    console.log(world);
+}
+// console.log(world);
+
+const aaron = "Aaron";
+console.log(aaron);
+
+// aaron = "Aaron Powell"