add build, npm, and codecov badge to readme

Author: jscottsmith

README.md

@@ -1,8 +1,8 @@
 # React Scroll Parallax
 
-Provides a React component and single passive scroll listener to add **vertical** scrolling based offsets to elements based on their position in the viewport. Works with universal (server-side rendered) React apps.
+[![npm version](https://badge.fury.io/js/react-scroll-parallax.svg)](https://badge.fury.io/js/react-scroll-parallax) [![Build Status](https://travis-ci.org/jscottsmith/react-scroll-parallax.svg?branch=dev)](https://travis-ci.org/jscottsmith/react-scroll-parallax) [![codecov](https://codecov.io/gh/jscottsmith/react-scroll-parallax/branch/dev/graph/badge.svg)](https://codecov.io/gh/jscottsmith/react-scroll-parallax)
 
-[View on NPM](https://www.npmjs.com/package/react-scroll-parallax)
+Provides a React component and single passive scroll listener to add **vertical** scrolling based offsets to elements based on their position in the viewport. Works with universal (server-side rendered) React apps.
 
 ## Examples