The "simple option" was originally the note at the end of this section about
using the SSM web console.  That link changed, but we also discovered that you
have to have created a parameter in that region yourself to be able to use the
search quicklink.  Requiring that would be awkward, so we remove the link.

A simpler option for most people is to use the resolve:ssm: prefix to have EC2
dynamically fetch the latest AMI ID from SSM.  This updates the wording to
prefer that option, creating a new subsection for manually fetching parameters.

This was put in for completeness, but goes against the purpose of the
quickstart guides, which is to get an interested user launching Bottlerocket
quickly, and it's awkward to word such a different purpose here.

The BUILDING guide is linked from README right after the links to the
quickstart guides, for users that have more advanced needs and need to build
their own images.