gen_compile_commands: reword the help message of -d option

I think the help message of the -d option is somewhat misleading.

  Path to the kernel source directory to search (defaults to the working directory)

The part "kernel source directory" is the source of the confusion.
Some people misunderstand as if this script did not support separate
output directories.

Actually, this script also works for out-of-tree builds. You can
use the -d option to point to the object output directory, not to
the source directory. It should match to the O= option used in the
previous kernel build, and then appears in the "directory" field of
compile_commands.json.

Reword the help message.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/gen_compile_commands.py

@@ -31,13 +31,13 @@ def parse_arguments():
 
     Returns:
         log_level: A logging level to filter log output.
-        directory: The directory to search for .cmd files.
+        directory: The work directory where the objects were built.
         output: Where to write the compile-commands JSON file.
     """
     usage = 'Creates a compile_commands.json database from kernel .cmd files'
     parser = argparse.ArgumentParser(description=usage)
 
-    directory_help = ('Path to the kernel source directory to search '
+    directory_help = ('specify the output directory used for the kernel build '
                       '(defaults to the working directory)')
     parser.add_argument('-d', '--directory', type=str, help=directory_help)