add: usage param

README.md

@@ -3,8 +3,45 @@
 NNST: Network Scan Tools
 
 ## Status
+
 Master: [![Build Status](https://travis-ci.org/kekeho/nnst.svg?branch=master)](https://travis-ci.org/kekeho/nnst)
 
+## Features
+
+### Port scan
+
+Scan unix port (parallel), and check port is open.
+
+## Usage
+
+```sh
+   _  ___  ____________
+  / |/ / |/ / __/_  __/
+ /    /    /\ \  / /
+/_/|_/_/|_/___/ /_/
+
+NNST: Network Scan Tools
+
+Usage:
+    nnst portscan [-t=<timeout>] <address> <ports>...
+    nnst portscan [-t=<timeout>] <address> -r <start_port> <end_port>
+
+Command:
+    portscan: Check port(s) open
+
+
+Options:
+    address                     Target address (hostname, domain or IP)
+    ports                       Target port list
+    -t --timeout=<timeout>      Set timeout [ms] (default=2500)
+
+    -r --range                  Range mode
+    <start_port>, <end_port>    Set scan range
+
+    -h --help                   Show this help
+    -v --version                Show version info
+```
+
 ## Build
 
 ### Dependencies to build