git: openjdk/amber-docs: Update cross refs

[duke]

Changeset: d6c3ab4f
Author:    briangoetz <brian at briangoetz.com>
Date:      2021-05-19 15:01:29 +0000
URL:       https://git.openjdk.java.net/amber-docs/commit/d6c3ab4f50a8393defa02c9cb4de790240415025

Update cross refs

! site/index.md