<iframe src="[[[ICLOUD URL GOES HERE]]]?embed=true" width="640" height="500" frameborder="0" allowfullscreen="1" referrer="no-referrer"></iframe>

Here’s the basic formula:

So my example now looks like this:

<iframe src="https://www.icloud.com/keynote/0BnBgSWdHQbQDKsC4gq1mUbZA?embed=true" width="640" height="500" frameborder="0" allowfullscreen="1" referrer="no-referrer"></iframe>

You may want to tweak the width and height numbers to suit your needs. Apple made them 100% and 100%, but that isn’t going to work for this kind of context.