Hard to find samples for "Load more and infinite scroll" section of amp-list

[Load more and infinite scroll](https://amp.dev/documentation/components/amp-list/?format=websites#load-more-and-infinite-scroll)

I realized the sample for this is [Show More Button](https://amp.dev/documentation/examples/interactivity-dynamic-content/show_more_button/) but it took me a while to find it. The examples linked to from the component page are the ones in amphtml which can't be easily tested (they use a unit test endpoint) and [the component](https://amp.dev/documentation/examples/components/amp-list/?format=websites) example makes no mention of this (maybe we need to update it?).