add htaccess files and index.php with slim instantiation

public/.htaccess

@@ -0,0 +1,4 @@
+RewriteEngine On
+RewriteCond %{REQUEST_FILENAME} !-f
+RewriteCond %{REQUEST_FILENAME} !-d
+RewriteRule ^ index.php [QSA,L]

public/index.php

@@ -0,0 +1,16 @@
+<?php
+
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\RequestInterface as Request;
+use Slim\Factory\AppFactory;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+$app = AppFactory::create();
+
+$app->get('/', function (Request $request, Response $response, $args) {
+    $response->getBody()->write("Hello world!");
+    return $response;
+});
+
+$app->run();