docs(readme): Fix markdown error (#227)

README contained unescaped & unclosed `<style>` tag that made almost the whole
README unreadable on the npm package page; see:
https://www.npmjs.com/package/style-loader

This is a good test page to see how READMEs will display on npm:
https://revin.github.io/marky-markdown/

Author: mgol

README.md

@@ -9,7 +9,7 @@
       src="https://webpack.js.org/assets/icon-square-big.svg">
   </a>
   <h1>Style Loader</h1>
-  <p>Adds CSS to the DOM by injecting a `<style>` tag</p>
+  <p>Adds CSS to the DOM by injecting a `&lt;style&gt;` tag</p>
 </div>
 
 <h2 align="center">Install</h2>