docs: add documentation for makefile

Signed-off-by: Rodney Osodo <[email protected]>

Makefile

@@ -49,11 +49,11 @@ help:
 	@echo "Usage: make <target>"
 	@echo ""
 	@echo "Targets:"
-	@echo "  build:         build the binary"
-	@echo "  install:       install the binary"
-	@echo "  all:           build the binary"
-	@echo "  clean:         clean the build directory"
-	@echo "  lint:          run golangci-lint"
+	@echo "  <service>:        build the binary for the service i.e manager, proplet, cli"
+	@echo "  all:              build all binaries i.e manager, proplet, cli"
+	@echo "  install:          install the binary i.e copies to GOBIN"
+	@echo "  clean:            clean the build directory"
+	@echo "  lint:             run golangci-lint"
 	@echo "  start-magistrala: start the magistrala docker compose"
 	@echo "  stop-magistrala:  stop the magistrala docker compose"
-	@echo "  help:          display this help message"
+	@echo "  help:             display this help message"