Merge branch 'prism-readme-how-to' into 'master'

Add at the readme instructions about how to use the PRISM library.

See merge request agaric/sites/agaric-com!58

README.md

@@ -80,3 +80,16 @@ Commit the files with a message on what you deployed with  'git commit -m '
 Push the changes to the repo with `git push`
 
 If you need to overwrite live configuration (only after confirming you've committed any parts you want to keep) you can use ahoy for that too with `deploy-site-force`.
+
+## Code Hightlight.
+
+The [prism.js](https://prismjs.com/) library was added in the site and can be used like this:
+
+```
+<pre>
+  <code class="language-css">
+    p { color: red }
+  </code>
+</pre>
+```
+The suffix of the class needs to be changed depending of the language that is going to be highlighted eg: `language-php`,  `language-js` etc.