feat(tvix/website): add structured data for search engines

This closes b/303.

Change-Id: Icaeccba23a2590c22106bed6e859ed3188c87a02
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9540
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Autosubmit: tazjin <tazjin@tvl.su>

tvix/website/default.nix

@@ -1,6 +1,21 @@
 { depot, lib, pkgs, ... }:
 
 let
+  description = "Rust implementation of the purely-functional Nix package manager";
+
+  # https://developers.google.com/search/docs/advanced/structured-data/
+  # https://schema.org/SoftwareApplication
+  structuredData = {
+    "@context" = "https://schema.org";
+    "@type" = "SoftwareApplication";
+    name = "Tvix";
+    url = "https://tvix.dev";
+    abstract = description;
+    applicationCategory = "DeveloperApplication";
+    contributor = "https://tvl.fyi";
+    image = "https://tvix.dev/logo.webp";
+  };
+
   # All Tvix-related blog posts from the main TVL website
   tvixPosts = builtins.filter
     (post: !(post.draft or false) && (lib.hasInfix "Tvix" post.title))
@@ -14,6 +29,13 @@ let
       ${builtins.readFile ./landing-en.md}
       ${builtins.concatStringsSep "\n" postListEntries}
     '';
+
+    extraHead = ''
+      <meta name="description" content="${description}">
+      <script type="application/ld+json">
+        ${builtins.toJSON structuredData}
+      </script>
+    '';
   };
 
 in