Kubernetes makefile: add usage example (#1244)

Document how to target particular releases (apps) with helmfile command

Related PR/s
* https://git.speag.com/oSparc/osparc-ops-deployment-configuration/-/merge_requests/1640

Author: YuryHrytsuk

charts/Makefile

@@ -11,9 +11,15 @@ include $(REPO_CONFIG_LOCATION)
 export CONFIG_DIR := $(shell dirname $(REPO_CONFIG_LOCATION))
 CHART_DIRS := $(wildcard $(REPO_BASE_DIR)/charts/*/)
 
+# Example of usage:
+# make helmfile-diff HELMFILE_EXTRA_ARGS='--selector app=adminer'
 HELMFILE_EXTRA_ARGS ?=
 HELMFILE := helmfile $(HELMFILE_EXTRA_ARGS)
 
+#
+# Targets
+#
+
 .PHONY: .check-helmfile-installed
 .check-helmfile-installed: ## Checks if helmfile is installed
 	@if ! command -v helmfile >/dev/null 2>&1; then \