Add Makefile

Signed-off-by: dusanb <borovcanindusan1@gmail.com.com>

Author: dusanb

Makefile

@@ -0,0 +1,4 @@
+all:
+	CGO_ENABLED=0 GOOS=linux go build -mod=vendor -ldflags "-s -w" -o build/coap-cli-linux cmd/main.go
+	CGO_ENABLED=0 GOOS=darwin go build -mod=vendor -ldflags "-s -w" -o build/coap-cli-darwin cmd/main.go
+	CGO_ENABLED=0 GOOS=windows go build -mod=vendor -ldflags "-s -w" -o build/coap-cli-windows cmd/main.go