add a book count

frontend/files/app.js

@@ -39,6 +39,9 @@ function renderTable(books, sortField) {
   var bookElement = document.getElementById("books");
   bookElement.innerHTML = TableTemplate(books);
 
+  var bookCount = document.getElementById("bookCount");
+  bookCount.innerHTML = `${books.length} books`;
+
   // add listeners for selecting book to view
   Array.from(bookElement.querySelectorAll("tbody tr"))
     .slice(1) // remove header from Array