Add selector section in sidebar and make changes to the section

Author: zsid

docs/README.md

@@ -5,6 +5,8 @@
   - [Basic Tutorial](./introduction/basic-tutorial.md)
 - Using React-Redux
   - [Connect: Extracting Data with `mapStateToProps`](./using-react-redux/connect-extracting-data-with-mapStateToProps.md)
+  - [Connect: Dispatching Actions with mapDispatchToProps](./using-react-redux/connect-dispatching-actions-with-mapDispatchToProps.md)
+  - [Selector Functions](./using-react-redux/selector-functions.md)
 - [API](api.md#api)
   - [`<Provider store>`](api.md#provider-store)
   - [`connect([mapStateToProps], [mapDispatchToProps], [mergeProps], [options])`](api.md#connectmapstatetoprops-mapdispatchtoprops-mergeprops-options)