docs/daemon: replace deprecated '-g' option for '--data-root'

[thaJeztah]

addresses docker/docs#14056

[cpuguy83]

LGTM

[cpuguy83]

CI validation didn't like something.

[thaJeztah]

oooh, looks like we're somehow hitting the git:// brownout; does vndr default to using git:// protocol?

2022/01/11 11:24:19 Starting whole vndr cycle because no package specified
fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.

[thaJeztah]

CI is green now, but we should probably look at vndr for the 20.10 branches at least

[elfranne]

Thanks !

[thaJeztah]

yw! This won't be published yet until it's cherry-picked into the 20.10 release branch, but I'll likely do a round of documentation cherry-picks later this week