Offering a PRO version for a plugin?

Hi there, I'm working on a wordpress plugin called Ninja Bar,
here is the snick peak: https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-xtf1/v/t1.0-9/11391276_960454720645672_1171443193945394510_n.jpg?oh=e4707ff0c549a4db33678672609d9e2e&oe=5631264B&__gda__=1441901328_85464cae384688e6c2d068ca9b6855c1

And I would like to offer a free (lite) and a premium (pro) version of it.
Now, the questions are next:

Thank you in advance.

You can add PRO version to purchase here.

But, you can write a url to allow customers to install free-demo version in the plugin description.