(readme): enabled syntax highlighting for js

README.md

@@ -122,17 +122,21 @@ To use MathJax components in a node application, install the `mathjax` package:
 
 Then require `mathjax` within your application:
 
-    require('mathjax').init({ ... }).then((MathJax) => { ... });
+```js
+require('mathjax').init({ ... }).then((MathJax) => { ... });
+```
 
 where the first `{ ... }` is a MathJax configuration, and the second
 `{ ... }` is the code to run after MathJax has been loaded.  E.g.
 
-    require('mathjax').init({
-      loader: {load: ['input/tex', 'output/svg']}
-    }).then((MathJax) => {
-      const svg = MathJax.tex2svg('\\frac{1}{x^2-1}', {display: true});
-      console.log(MathJax.startup.adaptor.outerHTML(svg));
-    }).catch((err) => console.log(err.message));
+```js
+require('mathjax').init({
+  loader: {load: ['input/tex', 'output/svg']}
+}).then((MathJax) => {
+  const svg = MathJax.tex2svg('\\frac{1}{x^2-1}', {display: true});
+  console.log(MathJax.startup.adaptor.outerHTML(svg));
+}).catch((err) => console.log(err.message));
+```
 
 
 See the