Add example illustrating the use of skip links

[mefechoel]

Svelte Navigator gives you a lot of accessibility improvements out of the box, but for an even better experience the user needs to tailor focus management manually.

A common and apparently very useful technique to improve a11y is the usage of skip links.
This is described further in this blog post by Marcy Sutton on the results of user testing different a11y approaches.

It might not be obvious how to implement the technique with Svelte Navigator, so it should be broken down in an example.