[add] readme file with usage documentation

Author: Sergio Daniel Xalambrí

README.md

@@ -0,0 +1,67 @@
+# react-url
+A React.js High-Order Component and decorator for parsing and resolving URLs inside your application.
+
+## Installation
+```bash
+npm i -S react react-url
+```
+
+## API
+### URLProvider
+```javascript
+import { render } from 'react-dom';
+import { URLProvider } from 'react-url';
+
+import App from './containers/App';
+
+const urls = {
+  profile: '/profile/:username/',
+};
+
+render(
+  <URLProvider urls={urls}>
+    <App />
+  </URLProvider>,
+  document.body,
+);
+```
+* `URLProvider` is a High-Order Components
+* `URLProvider` expect only one property named `urls`.
+* `urls` should be an object where the keys are the URLs names and the values are the unparsed url using the sintax of Express.js.
+
+### connectURL
+```javascript
+import React, { Component } from 'react';
+import { connectURL } from 'react-url';
+
+function mapURLToProps(getURL, props) {
+  return {
+    profileURL: getURL('profile', { username: props.username }),
+  };
+}
+
+@connectURL(mapURLToProps)
+class UserData extends Component { ... }
+
+export default UserData;
+```
+* The `connectURL` it's optional.
+* If you don't supply it then it will add the `getURL` function as a property.
+* The `mapURLToProps` function will receive the `getURL` function and `props` object as parameter and should return an object.
+* You can use it as a decorator (like the example above) or just as a function and send them the component to connect.
+
+### parser
+```javascript
+import { parser } from 'react-url';
+
+const urls = {
+  profile: '/profile/:username/',
+};
+
+const profileURL = parser(urls, 'profile', {
+  username: 'sergiodxa',
+});
+```
+* This is a Low-Level API and this used internally for the `connectURL` decorator, it's not expected that you should use it.
+* `parser` receive as arguments the `urls` map, the url name and the options/parameters object.
+* It will return the final parsed url string.