git: openjdk/amber-docs: Update towards-better-serialization.md

[duke]

Changeset: 13a4aac1
Author:    Brian Goetz <brian at briangoetz.com>
Committer: GitHub <noreply at github.com>
Date:      2020-08-06 10:10:37 +0000
URL:       https://git.openjdk.java.net/amber-docs/commit/13a4aac1

Update towards-better-serialization.md

Update broken links

! site/design-notes/towards-better-serialization.md