add API key instructions to README

Author: Sab44

README.md

@@ -7,6 +7,12 @@ Please report any issues with the client here: https://github.com/pyload/pyload-
 
 In order to use the Android client make sure the newest pyLoad Core with version 0.5 and up is running on your system, accessible over the network, the ip/hostname is correct, and the port forwarded if necessary.
 
+#### Generate an API key
+
+You need an API key to connect the app to your pyLoad instance. Open pyLoad in your browser and navigate to:  
+**Settings** → **Users** → Next to your username tap on **Actions** → **Manage API Keys** → **Generate**.  
+Make sure to copy the API key when it is shown as you will not be able to view it again after closing the dialog.
+
 #### Features
 - Modern UI (Android 4+ components)
 - **ActionBar** integration