Recommend --config-cache for configure

[hugovk]

Describe the enhancement or feature you would like

Using --config-cache with configure makes it much quicker: 3s cached vs 39s without on my machine.

Some example wasm commands include it, but shall we include it by default in the other relevant commands on that page, and the front page?

Describe alternatives you have considered

Status quo, builds are slower. Or only include it in the getting-started/setup-building page if there's some reason not to put in on the front page.

Additional context

Not everyone knows about this option: python/cpython#133027 (comment)