Add blueprint to HTML Builders section

[stephannv]

Link

https://github.com/gunbolt/blueprint

Checklist

• [X] - Shard is at least 30 days old.
• [X] - Shard has CI implemented.
• [X] - Shard has daily/weekly periodic builds (ideally with Crystal latest and nightly).

[Blacksmoke16]

I think HTML Builders section would be more appropriate.

[stephannv]

Done @Blacksmoke16. I put on Template Engine because I saw Water gem there. But makes sense to put it on HTML Builders section.