SWPROT-8953: build: Add hints in helper script

This part is not yet documented in docs,
it will be done after the deduplication of UnifySDK

Origin: #35
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

helper.mk

@@ -87,15 +87,19 @@ endif
 
 
 help: README.md
-	@cat $<
+	@head $<
 	@echo ""
+	@echo "# Usage"
+	@echo "#  ./helper.mk setup # To setup developer system (once)"
+	@echo "#  ./helper.mk # Build once system has been setup"
 	@echo "# Available rules at your own risk:"
 	@grep -o '^[^ ]*:' ${SELF} \
 		| grep -v '\$$' | grep -v '^#' | grep -v '^\.' \
 		| grep -v '=' | grep -v '%'
 	@echo ""
 	@echo "# Environment:"
-	@echo "# PATH=${PATH}"
+	@echo "#  PATH=${PATH}"
+	@echo "#  version=${version}"
 	@echo ""
 
 setup/debian: ${CURDIR}/docker/target_dependencies.apt ${CURDIR}/docker/host_dependencies.apt