update Docker startup steps

[taroface]

Fixes #9185.

[cockroach-teamcity]

This change is 

[taroface]

@jbowens I went as far back as 19.2 to make this fix, but let know if that wasn't necessary.

Also, these articles are used in our Linux tutorials (e.g. https://www.cockroachlabs.com/docs/v20.2/start-a-local-cluster-in-docker-linux) as well. Can the same updates apply to Linux, or should we break this out into a Mac-specific article?

[cockroach-teamcity]

Online preview: http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/9a8981a29736813f2c0e3c7d827af792de776236/

[jbowens]

Looks good! I think it's good idea to make the change all the way back to 19.2.

Can the same updates apply to Linux, or should we break this out into a Mac-specific article?

Yeah, that seems fine to recommend the same for Linux.

I think one more thing we should change is Step 6: Stop the cluster. Instead of telling them to rm -rf cockroach-data, we should tell them to remove the Docker volumes:

docker volume rm roachdb1 roachdb2 roachdb3

[taroface]

TFTR!

[cockroach-teamcity]

Online preview: http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/a67c4372b57b1018d55ce5cff9ecfb98fff06060/

[jbowens]

lgtm!

[mikeCRL]

LGTM

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @mikeCRL)

[jseldess]

@taroface, I'll go ahead and merge this. If there's any work left, you can follow-up with another PR.