Add Dockerfile left-hand navigation

[thaJeztah]

I had this branch on my machine as a "draft", but looks like I never opened a PR for it (might be I was still working on it). In any case, let me push this as a PR to test it (and see if more is needed to make it work)

Alternative to https://github.com/docker/docker.github.io/pull/12883 closes https://github.com/docker/docker.github.io/pull/12883

[netlify[bot]]

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[usha-mandya]

@thaJeztah Unable to click on the commands on the left nav in Netlify. Is this expected?

[thaJeztah]

Oh! Of course; yes, that's because the builder.md is fetched from upstream.

I need to test this again locally; I had it in a "WIP" branch, so possibly there's things broken still (opened because I got pinged on https://github.com/docker/docker.github.io/pull/12883, and recalled I had this branch)

[docker-robott]

Thanks for the pull request. We'd like to make our product docs better, but haven’t been able to review all the suggestions. As our docs have also diverged, we do not have the bandwidth to review and rebase old pull requests.

If the updates are still relevant, review our contribution guidelines and rebase your pull request against the latest version of the docs, then mark it as fresh with a /remove-lifecycle stale comment. If not, this pull request will be closed in 30 days. This helps our maintainers focus on the active pull requests.

Prevent pull requests from auto-closing with a /lifecycle frozen comment.

/lifecycle stale