update makefile

Makefile

@@ -0,0 +1,17 @@
+BIN_DIR=_output/cmd/bin
+
+all: init build
+
+build: init
+	go build -o ${BIN_DIR}/gotgt gotgt.go
+
+verify:
+	hack/verify-gofmt.sh
+
+init:
+	mkdir -p ${BIN_DIR}
+clean:
+	rm -fr ${BIN_DIR}
+
+.PHONY: clean
+