Improve user-experience

README.md

-config generator:
- - change addrNum - the number of address to be generated
+# Command:
+    `npm run gen <array-size>`
 
-run:
- - node generate.js
+# An xample:
+
+    `npm run gen 1000`

generate.js

 var ethers = require('ethers');  
 var crypto = require('crypto');
-var addrNum = 500;
+
+// take the third argument
+var addrNum = process.argv.slice(2);
 var s = "";
 
 for (let i = 0; i < addrNum; i++) { 

package.json

@@ -4,7 +4,8 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "gen": "node generate.js"
   },
   "repository": {
     "type": "git",