Broken link to https://spring.io/guides/gs/spring-boot-docker

This guide links https://spring.io/guides/gs/spring-boot-docker , but that URL now results in 404 not found.

```adoc
NOTE: There is also a Getting Started Guide on https://spring.io/guides/gs/spring-boot-docker[Docker], which would also be a good starting point, but it does not cover the range of choices that we cover here or cover them in as much detail.
```