Replace Inaccessible URL in `codelist.txt` with Content from Eurostat

[maehr]

Current Behavior

The URL mentioned in codelist.txt is not accessible. It currently contains a TODO with a URL to Eurostat's metadata code lists.

Reproduction / Steps To Reproduce

1. Navigate to the docs folder.
2. Open codelist.txt.
3. See the TODO and inaccessible URL.

Anything else?

Suggested Changes

1. Replace the TODO and URL in codelist.txt with summarized content from Eurostat's Code Lists.
2. Include a reference to the Eurostat page for further details.

Content to Include

• Briefly describe what code lists are and their importance in statistical data.
• Mention that Eurostat uses around 600 code lists for various dimensions like age, sex, geo, time, and unit.
• Highlight the ongoing standardization efforts by Eurostat.

Benefits

• Provides a more informative and accessible resource for code lists.
• Aligns with reputable sources like Eurostat for metadata standards.

Tasks

• [ ] Update codelist.txt with summarized content from Eurostat.
• [ ] Add a reference to the Eurostat page.

[maehr]

@mtwente mentioned, that this feature is documented poorly.