title: added AFNetworking to new project got errors
body: <p>I created a new project, I simply dragged and dropped the <em>AFNetworking</em> folder into my project, and when I ran the project, I got these errors:</p>
  
  <pre><code>/Users/nadirahmed/Documents/iOS/afnet1/AFNetworking/AFNetworkReachabilityManager.h:40:1: Unknown type name 'NS_ASSUME_NONNULL_BEGIN'
  
  /Users/nadirahmed/Documents/iOS/afnet1/AFNetworking/AFNetworkReachabilityManager.h:51:1: Cannot combine with previous '(error)' declaration specifier
  
  /Users/nadirahmed/Documents/iOS/afnet1/AFNetworking/AFNetworkReachabilityManager.h:80:4: Pointer is missing a nullability type specifier (__nonnull or __nullable)
  </code></pre>
  
  <p>Here is what I tried:</p>
  
  <ul>
  <li>I cleaned the project  </li>
  <li>tried to drag and drop the library into different areas into the project  </li>
  <li>went to product, build</li>
  </ul>