Improve docs for TextDocument example

[emilk]

What

• Closes Text document archetype documentation doesn't render correctly #3904
• Closes Text document archetype documentation should document how component/entity links work #3905

This enabled the API-docs for the TextDocument example. To make sure it renders correctly I needed to:

• Remove the -code block (for proper embedding in the website inside of a markdown block)
• Replace """" with '''' in the python example, so it can be embedded in a """-docstring in the Python API docs

Python API docs:

Rust API docs:

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested demo.rerun.io (if applicable)
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

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