Provide a animated GIF into the README to show off the example app

What could be improved

We could add an animated GIF to show of the example app

Why should this be improved

More attractive to possible users

Any risks?

Not any

More information

• GIF: https://j.gifs.com/5QEyOB.gif
• YouTube: https://www.youtube.com/watch?v=KfRlWnWThMM

Possible implementation

Add the following code to the README section:

[![Twilio Unofficial Programmable Video Example](https://j.gifs.com/5QEyOB.gif)](https://gitlab.com/twilio-flutter-unofficial/programmable-video/-/tree/master/example "Twilio Unofficial Programmable Video Example")

This will produce: