Copy the launcher script into linux-package

The launcher script is mostly useless on linux, but is needed
when using kitty.app built from source and might be useful on linux as
well, if running kitty without putting it on PATH.

setup.py

@@ -521,6 +521,7 @@ def package(args, for_bundle=False, sh_launcher=False):  # {{{
         for f in files:
             path = os.path.join(root, f)
             os.chmod(path, 0o755 if f.endswith('.so') else 0o644)
+    shutil.copy2('kitty/launcher/kitty', os.path.join(libdir, 'kitty', 'launcher'))
     launcher_dir = os.path.join(ddir, 'bin')
     safe_makedirs(launcher_dir)
     build_linux_launcher(args, launcher_dir, for_bundle, sh_launcher)