init blog table

public/index.php

@@ -65,6 +65,7 @@ $app->get('/', function (Request $request, Response $response, array $args) {
 
 $app->map(['GET', 'POST'], '/blog/create', function (Request $request, Response $response, array $args) {
     if (isset($_SESSION['username'])) {
+        global $db;
         if ($request->getMethod() == 'GET') {
             addNavbar($response);
             $response->getBody()->write('<form action="/blog/create" method="POST">');