Update jest.md

[Eji4h]

I add demo for easy to understand.

[dmurvihill]

Hi @Eji4h, thanks for the contribution.

This repo is no longer used (see #160) but I have opened a new PR on my fork. Cheers.

[dmurvihill]

@Eji4h, would you be willing to clarify this example? The file is hard to understand, but simply adding another pile of undocumented code is not helping me understand. Cheers.