update readme

Author: j2doll

README.md

@@ -1,19 +1,38 @@
 # json-downloader
 
-## What is it?
-- Downloader for Windows Console
-	- It is written for personal purpose.
-- DONE:
-	- Ability to download files continuously
-	- Getting a download list from a json file
-- TODO:
-	- Extract files from compressed files	
+## Introduction
+- File Downloader for Windows Console
+- It is written for personal purpose.
+
+### DONE
+- Ability to download files continuously
+- Getting a download list from a json file
+
+### TODO
+- Extract files from compressed files	
+
+## How to use program
+- Execute 'json-downloader.exe' with json parameter 
+```cmd
+json-downloader.exe data.json
+```
+
+### Json file format
+- The json file(such as data.json) consists of the following:
+```json
+{
+	"https://raw.githubusercontent.com/j2doll/json-downloader/master/README.md" : "README.md" ,
+	"https://raw.githubusercontent.com/j2doll/json-downloader/master/LICENSE" : "LICENSE" 
+}
+```
+- The first argument is the URL of the file you want to download.
+- The second argument is the name of the file to be saved locally.
 
 ## Requred Environment
 - Visual Studio 2017 x64
 - Windows 10 x64 (Maybe it will also build on Windows 7/8 x64.)
 
-## License
+## License and links
 - json-downloader is under GPL 3 license. [https://github.com/j2doll/json-downloader](https://github.com/j2doll/json-downloader)
 - curl is under MIT style license. [https://curl.haxx.se/docs/copyright.html](https://curl.haxx.se/docs/copyright.html)
 - JSON for Modern C++ is under MIT license. [https://github.com/nlohmann/json/releases](https://github.com/nlohmann/json/releases)