Enable Auto-Transition

[busypeoples]

Add a settings option to define auto-transitions.
The autoTransition constant needs to define the transition time in seconds, i.e.

// index.mdx

export const autoTransition = 5

Also see comment by @tomByrer in #75

[busypeoples]

A possible documentation:

Auto Transition

To enable the automatic transitioning of your slides and appears, export a autoTransition constant.
autoTransition should set the time between transitions.
For example if you need to transition every 10 seconds, add the following to your MDX file:

// Example index.mdx

export const autoTransition = 10