kbuild: document versioncheck in make help

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

diff --git a/Makefile b/Makefile
index 2101e41..d0ffbeb 100644
--- a/Makefile
+++ b/Makefile
@@ -1188,6 +1188,7 @@
 	@echo  'Static analysers'
 	@echo  '  checkstack      - Generate a list of stack hogs'
 	@echo  '  namespacecheck  - Name space analysis on compiled kernel'
+	@echo  '  versioncheck    - Sanity check on version.h usage'
 	@echo  '  includecheck    - Check for duplicate included header files'
 	@echo  '  export_report   - List the usages of all exported symbols'
 	@if [ -r $(srctree)/include/asm-$(SRCARCH)/Kbuild ]; then \