Update penguin classification to technique example (Py data loader)

[allisonhorst]

• Renames directory to /loader-python-to-csv
• Updates index.md to match structure/length/style of other technique examples
• Updates README (for this example, and examples overview page)
• Tests new pattern for including virtual environment setup in copyable chunks
• Live version: https://observablehq.observablehq.cloud/framework-example-loader-python-to-csv/

[Fil]

Is it a requirement to keep the URL? I think I'd prefer we use a new predictable URL https://observablehq.observablehq.cloud/framework-example-loader-python-to-csv/ and possibly deploy in the old URL a single file that redirects.

Other than that LGTM

[mbostock]

I think platform supports redirects natively so you can just change the slug in the UI.