Add README for the npm package

Fix #242.

Author: zalmoxisus

npm-package/README.md

@@ -0,0 +1,38 @@
+# Redux DevTools Extension's helper
+
+[![Join the chat at https://gitter.im/zalmoxisus/redux-devtools-extension](https://badges.gitter.im/zalmoxisus/redux-devtools-extension.svg)](https://gitter.im/zalmoxisus/redux-devtools-extension?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
+## Usage
+
+  Install:
+  ```
+  npm install --save redux-devtools-extension
+  ```
+  and use like that:
+  ```js
+  import { createStore, applyMiddleware } from 'redux';
+  import { composeWithDevTools } from 'redux-devtools-extension';
+
+  const store = createStore(reducer, composeWithDevTools(
+    applyMiddleware(...middleware),
+    // other store enhancers if any
+  ));
+  ```
+  or if needed to apply [extension’s options](https://github.com/zalmoxisus/redux-devtools-extension/blob/master/docs/API/Arguments.md#windowdevtoolsextensionconfig):
+  ```js
+  import { createStore, applyMiddleware } from 'redux';
+  import { composeWithDevTools } from 'redux-devtools-extension';
+
+  const composeEnhancers = composeWithDevTools({
+    // Specify here name, actionsBlacklist, actionsCreators and other options
+  });
+  const store = createStore(reducer, composeEnhancers(
+    applyMiddleware(...middleware),
+    // other store enhancers if any
+  ));
+  ```  
+  There’re just [few lines of code](https://github.com/zalmoxisus/redux-devtools-extension/blob/master/npm-package/index.js). If you don’t want to allow the extension in production, just use ‘redux-devtools-extension/developmentOnly’ instead of ‘redux-devtools-extension’.
+
+## License
+
+MIT