kbuild: document 'make prepare' in 'make help'

The output of 'make help' covers a lot of options, but doesn't include
a listing for 'make prepare'.  Here's a one-liner to fix that...

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 698dfc6ba65c..6847464402aa 100644
--- a/Makefile
+++ b/Makefile
@@ -1181,6 +1181,7 @@ help:
         @echo  '  dir/            - Build all files in dir and below'
         @echo  '  dir/file.[ois]  - Build specified target only'
         @echo  '  dir/file.ko     - Build module including final link'
+        @echo  '  prepare         - Set up for building external modules'
         @echo  '  tags/TAGS       - Generate tags file for editors'
         @echo  '  cscope          - Generate cscope index'
         @echo  '  kernelrelease   - Output the release version string'