docs: add aztec-starter to `Examples`

[FilipHarald]

The examples in the docs are good in that they explain how everything works. However, they require the reader to do a lot of copy pasting. And added to that, they do not always work (1 & 2) this can be extremely frustrating.

I think it would be great to link to aztec-starter as it is a small independent repo easy for the user to just clone and play around with.