[Accessibility] Pretty-print code samples in the help guides

[eatyourgreens]

Help currently uses low quality screenshots of formatted code, like this one from the transcription guide.

I'm 90% sure mkdocs supports code formatting (possibly via a plugin), which would improve the readability and accessibility of these code examples. Something like the following example, in GitHub-flavoured markdown:

{
  "task": "T52",
  "task_label": null,
  "value": [
    {
      "task": "T15",
      "value": [
        {
          "select_label": "Sentenced (month)",
          "option": true,
          "value": 3,
          "label": "3 - March"
        }
      ]
    }
  ]
}

[eatyourgreens]

MKDocs code blocks answered enough of my questions to be able to open a PR.