docs: add nofollow to View as Markdown links.

[nisarhassan12]

Summary

• Adds rel="nofollow" to the "View as Markdown" links so HTML docs stop advertising /docs/markdown-docs/ URLs to crawlers.
• Crawl blocking lives in www-temporary, which owns https://materialize.com/robots.txt the remainder of the changes are made there.

[maheshwarip]

@nisarhassan12 should we add nofollow or should we mark the html as canonical? It's quite useful for agents search the web and land on our markdown docs when they can - what's the best practice here?

[nisarhassan12]

Thanks @maheshwarip Good call. I'll close this PR. The HTML pages already mark themselves as canonical, so Google should keep ranking /docs/... as the main result. nofollow on “View as Markdown” doesn’t really help with that, and it can make it harder for coding agents to notice the .md link.

The Google crawl-budget fix is the robots.txt change in www-temporary. I’d keep the HTML docs fully searchable, and only stop Google from crawling the raw .md copies as duplicates. People and agents can still open the markdown URL if they have the link.