Update a new readme file.

demo/electron/README.md

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+# React desktop Electron demo
+
+![TIM201907300143533f238.png](https://miao.su/images/2019/07/30/TIM201907300143533f238.png)
+
+## How to use
+
+First, enter the folder:
+
+```cd demo/electron```
+
+Install the libraries:
+
+```npm i``` or ```yarn``` (if you have been installed it)
+
+Build once:
+
+```npm run build```
+
+Then start the server:
+
+```npm run watch```
+
+Open another console at the same folder, and run this command to start the Electron process:
+
+```npm start```
+
+That's it!