kbuild: document INSTALL_MOD_PATH in 'make help'

	@echo  '  all		  - Build all targets marked with [*]'

	@echo  '* vmlinux	  - Build the bare kernel'

	@echo  '* modules	  - Build all modules'

	@echo  '  modules_install - Install all modules'

	@echo  '  modules_install - Install all modules to INSTALL_MOD_PATH (default: /)'

	@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'