MAINTAINERS: Add NSIS file for W32, W64 hosts

The NSIS installer configuration is maintained by me.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

MAINTAINERS

@@ -275,6 +275,7 @@ L: qemu-devel@nongnu.org
 M: Stefan Weil <sw@weilnetz.de>
 S: Maintained
 F: *win32*
+F: qemu.nsi
 
 ARM Machines
 ------------