Update docs

[optikalefx]

You need to prepare your interstitial every time you want to show it. Once you show it once, you can't show it again. This should be noted in the docs.

[optikalefx]

Instead, I think easiest practice is to just always prepare with autoShow:true

[floatinghotpot]

Yes, you need prepare before show. After a ad is dismissed, need prepare again.

As it will always need some time to load ad(depends on network speed), if use autoShow:true, it may delay a few seconds.

If call prepare to preload in the background, when you call show(), the ad can be displayed immediately.

[optikalefx]

Yea, I get that now, I think it should be more clear in the docs that you need to prepare every time you show an ad. Most people with ads show more than 1 ad, so they should know they need to prepare many times.