Readme: Added open() return value

README.md

@@ -27,6 +27,7 @@ DllCall("LoadLibrary", "Str", "OSC2AHK.dll", "Ptr")
 int open(HWND targetWindowHandle, unsigned int port);
 //targetWindowHandle: Handle to the calling window to which messages on received OSC data is sent
 //port: Network port to open
+//returns: Zero on success, something else on failure
 ```
 This opens the network port and enables the DLL to receive OSC messages.
 
@@ -34,7 +35,9 @@ Example AHK snippet:
 ```
 Gui +LastFound
 hWnd := WinExist()
-DllCall("OSC2AHK.dll\open", UInt, hWnd, UInt, 7002)
+success := DllCall("OSC2AHK.dll\open", UInt, hWnd, UInt, 7002)
+if (success != 0)
+    msgbox, Failed to open port!
 ```
 
 #### Close network port