generate-kde-frameworks.sh: fix helper script path

- Fix a bug in the script which prevented it from finding its helper script.
- Automatically redirect the output of the script to make it even easier
  to use.

maintainers/scripts/generate-kde-frameworks.sh

@@ -1,3 +1,5 @@
 #!/bin/sh
 
-./fetch-kde-qt.sh http://download.kde.org/stable/frameworks/5.24/ -A '*.tar.xz'
+./maintainers/scripts/fetch-kde-qt.sh \
+    http://download.kde.org/stable/frameworks/5.24/ -A '*.tar.xz' \
+    >pkgs/desktops/kde-5/frameworks/srcs.nix