Add instructions to add the `CFNetwork.framework` dependency

Without `CFNetwork.framework`, compilation fails with

```
Undefined symbols for architecture i386: "_CFHTTPMessageAppendBytes", "_CFHTTPMessageCopyAllHeaderFields", "_CFHTTPMessageCopyBody", "_CFHTTPMessageCreateEmpty", "_CFHTTPMessageGetResponseStatusCode", "_CFHTTPMessageIsHeaderComplete"
```
Add install instructions for CocoaPods