Add AI content usage preferences

All set to yes, so AI can freely use the content for training, search, and input.

Author: GBKS

robots.txt

@@ -40,4 +40,6 @@ Disallow: /docker-compose.yml
 Disallow: /Gemfile
 Disallow: /RAKEFILE
 
+Content-Signal: ai-train=yes, search=yes, ai-input=yes
+
 Sitemap: https://bitcoin.design/sitemap.xml