Add Docker installation to README installation

[jspeed-meyers]

Closes #259

Is this helpful? If not, should there be something else? Or should I simply close this issue and PR?

[kaniini]

In general, the hack scripts are replaced by ghcr.io/distroless/apko:latest, which does require Docker to run :)

I would recommend mentioning that instead of what is there presently, as its obsolete information now.

[jspeed-meyers]

That sounds good. I'm afraid I'll dork up the best way to explain this, so I've unassigned myself and will let someone more familiar with the project or documentation to make this change.

[amouat]

I added instructions to use the new Docker image in #311, which I think replaces this.

[jdolitsky]

closing as old/inactive. please re-open if necessary