improve help doc

Author: oiooj

README.md

@@ -19,14 +19,16 @@ A global proxy for go modules. see: [https://goproxy.io](https://goproxy.io)
 
 
 ### Proxy mode    
-    
+
     ./bin/goproxy -listen=0.0.0.0:80 -cacheDir=/tmp/test
 
     If you run `go get -v pkg` in the proxy machine, should set a new GOPATH which is different from the old GOPATH, or mayebe deadlock.
     See the file test/get_test.sh.
 
 ### Router mode    
 
+	./bin/goproxy -listen=0.0.0.0:80 -proxy https://goproxy.io
+
 Use the -proxy flag switch to "Router mode", which 
 implements route filter to routing private module 
 or public module .

main.go

@@ -48,9 +48,9 @@ var proxyHost string
 var excludeHost string
 
 func init() {
-	flag.StringVar(&excludeHost, "exclude", "", "exclude host pattern")
-	flag.StringVar(&proxyHost, "proxy", "", "next hop proxy for go modules")
-	flag.StringVar(&cacheDir, "cacheDir", "", "go modules cache dir")
+	flag.StringVar(&excludeHost, "exclude", "", "exclude host pattern, you can exclude internal Git services")
+	flag.StringVar(&proxyHost, "proxy", "", "next hop proxy for Go Modules, recommend use https://gopropxy.io")
+	flag.StringVar(&cacheDir, "cacheDir", "", "Go Modules cache dir, default is $GOPATH/pkg/mod/cache/download")
 	flag.StringVar(&listen, "listen", "0.0.0.0:8081", "service listen address")
 	flag.Parse()