set up demo, exercise, final folders

step1-06/exercise/src/components/TodoFooter.tsx

@@ -0,0 +1,11 @@
+import React from 'react';
+
+export const TodoFooter = (props: any) => {
+  const itemCount = Object.keys(props.todos).filter(id => !props.todos[id].completed).length;
+  return (
+    <footer>
+      <span>4 items left</span>
+      <button className="submit">Clear Completed</button>
+    </footer>
+  );
+};