docs(readme): add short description

Author: jdrouet

Diff for: README.md

@@ -1 +1,28 @@
 # Material UI theme editor
+
+## What is it made for?
+
+I'm a developer that loves to work with [MaterialUI](https://material-ui.com/) but it generates always the same looking websites.
+That's when a designer arrives and tell you "You've to use this color, and this color...", and it's a pain to integrate, you cannot make
+it fit with your MaterialUI theme, etc, just because your designer isn't really aware of what you use and what are the limits.
+
+So now, give this website to your designer, and wait for him to give you the theme file. And then, to integrate it, you just have to do
+the following
+
+```javascript
+import React from 'react';
+import ReactDOM from 'react-dom';
+import { createMuiTheme, MuiThemeProvider } from '@material-ui/core/styles';
+import Application from './your/entry/point';
+import yourRawTheme from './wherever/is/your/theme.json';
+
+const theme = createMuiTheme(yourRawTheme);
+
+ReactDOM.render(
+  <MuiThemeProvider theme={theme}>
+    <Application />
+  </MuiThemeProvider>
+, document.getElementById('root'));
+```
+
+And BOOOM! You have a nice theme, you designer is happy, and you didn't fight with him/her...