build(Makefile): add documentation

Makefile

@@ -94,11 +94,13 @@ release:
 	git push origin $${VERSION}
 
 .PHONY: compile
+# HELP: perform full compilation (frontend and backend)
 compile:
 	$(MAKE) compile-frontend
 	$(MAKE) compile-backend
 
 .PHONY: start
+# HELP: start complete development environment with a fresh test database
 start:
 	$(MAKE) start-postgres
 	$(MAKE) start-memcached