Add notice to anything under /archive

[bmaupin]

Is there a way we can add some kind of banner to everything under /archive? Something like:

⚠️ Archived content

The content you're reading has been explicitly archived because it is no longer maintained or known to be outdated, irrelevant, or incorrect.

[bmaupin]

Markdown admonitions don't seem to be supported by Jekyll's default markdown library (kramdown): https://github.com/gettalong/kramdown/issues/300

So we'll need to implement this ourselves.

[bmaupin]

Some ideas:

• https://github.com/pmarsceill/just-the-docs/issues/171
• https://sphinx-rtd-theme.readthedocs.io/en/latest/demo/demo.html#admonitions