Merge pull request hakimel#1823 from gilxa1226/master

Update to README.md for PDF printing

Author: hakimel

README.md

@@ -847,6 +847,19 @@ Reveal.initialize({
 Presentations can be exported to PDF via a special print stylesheet. This feature requires that you use [Google Chrome](http://google.com/chrome) or [Chromium](https://www.chromium.org/Home) and to be serving the presention from a webserver.
 Here's an example of an exported presentation that's been uploaded to SlideShare: http://www.slideshare.net/hakimel/revealjs-300.
 
+In order to enable PDF print capability in your presentation, the following code must be inserted in the HEAD section of your HTML document.
+
+```html
+<!-- Printing and PDF exports -->
+<script>
+	var link = document.createElement( 'link' );
+	link.rel = 'stylesheet';
+	link.type = 'text/css';
+	link.href = window.location.search.match( /print-pdf/gi ) ? 'css/print/pdf.css' : 'css/print/paper.css';
+	document.getElementsByTagName( 'head' )[0].appendChild( link );
+</script>
+```
+
 Export dimensions are inferred from the configured [presentation size](#presentation-size). Slides that are too tall to fit within a single page will expand onto multiple pages. You can limit how many pages a slide may expand onto using the `pdfMaxPagesPerSlide` config option, for example `Reveal.configure({ pdfMaxPagesPerSlide: 1 })` ensures that no slide ever grows to more than one printed page.
 
 1. Open your presentation with `print-pdf` included in the query string i.e. http://localhost:8000/?print-pdf#/. This triggers the default index HTML to load the PDF print stylesheet ([css/print/pdf.css](https://github.com/hakimel/reveal.js/blob/master/css/print/pdf.css)). You can test this with [lab.hakim.se/reveal-js?print-pdf](http://lab.hakim.se/reveal-js?print-pdf).