Update offline mode readme

Author: nonelse

README.md

@@ -273,6 +273,26 @@ Adjust.setEnabled(false);
 You can verify if the adjust SDK is currently active with the method `isEnabled`. It is always possible
 to activate the adjust SDK by invoking `setEnabled` with the `enabled` parameter set to `true`.
 
+### 11. Offline mode
+
+You can put the adjust SDK in offline mode to suspend transmission to our servers, 
+while retaining tracked data to be sent later. While in offline mode, all information is saved
+in a file, so be careful not to trigger too many events while in offline mode.
+
+You can activate offline mode by calling `setOfflineMode` with the parameter `true`.
+
+```cs
+Adjust.setOfflineMode(true);
+```
+
+Conversely, you can deactivate offline mode by calling `setOfflineMode` with `false`.
+When the adjust SDK is put back in online mode, all saved information is send to our servers 
+with the correct time information.
+
+Unlike disabling tracking, this setting is *not remembered*
+bettween sessions. This means that the SDK is in online mode whenever it is started,
+even if the app was terminated in offline mode.
+
 ## Troubleshooting
 
 ### iOS