Update README.md

Author: afshinm

README.md

@@ -6,11 +6,17 @@ A better way for new feature introduction and step-by-step users guide for your
 ##How to use
 Simple 3 steps.
 
-1) Include `intro.js` and `introjs.css` (or minified version for production) in your page.
+**1)** Include `intro.js` and `introjs.css` (or minified version for production) in your page.
 
-2) Add `data-intro` and `data-step` to your HTML elements.  
+**2)** Add `data-intro` and `data-step` to your HTML elements.  
 For example: 
 ```html
 <a href='http://google.com/' data-intro='Hello step one!' data-step='1'></a>
 ````
 
+**3)** Call this JavaScript function:
+```javascript
+introJs().start();
+````
+ 
+Also you can pass one parameter to `introJs` function to limit the presentation section, for example `introJs(".introduction-farm").start();` runs the introduction only for elements with `class='introduction-farm'`.