You could just use CONFIG += embed_manifest_exe
though, but in essence you need to put the manifest file beside your executable and the last line seems to take care of that.
That is, it is adding a manifest to your "Hello.exe" executable file.
If you do not happen to know what manifest files are, then you can read the MSDN documentation below, but in short: they are carrying run time information for your executable in this particular case:
http://msdn.microsoft.com/en-us/library/aa374191(v=vs.85).aspx