[chore] Update the Makefile

Makefile

@@ -1,17 +1,14 @@
 
-REPORTER = dot
+help: ## print this message
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-20s\033[0m %s\n", $$1, $$2}'
 
-test:
+test: ## run tests either in the browser or in Node.js, based on the `BROWSERS` variable
 	@if [ "x$(BROWSERS)" = "x" ]; then make test-node; else make test-zuul; fi
 
-test-node:
-	@./node_modules/.bin/mocha \
-		--reporter $(REPORTER) \
-		--bail \
-		test/index.js
+test-node: ## run tests in Node.js
+	@./node_modules/.bin/mocha --reporter dot --bail test/index.js
 
-test-zuul:
-	@./node_modules/zuul/bin/zuul \
-		test/index.js
+test-zuul: ## run tests in the browser
+	@./node_modules/zuul/bin/zuul test/index.js
 
-.PHONY: test
+.PHONY: help test test-node test-zuul