config the header, seed images of radicle seed server

pkgs/radicle-explorer/default.nix

@@ -0,0 +1,32 @@
+{pkgs, ...}:
+(pkgs.radicle-explorer.withConfig {
+  preferredSeeds = [
+    {
+      hostname = "seed.youthlic.fun";
+      port = 443;
+      scheme = "https";
+    }
+    {
+      hostname = "ash.radicle.garden";
+      port = 443;
+      scheme = "https";
+    }
+    {
+      hostname = "seed.radicle.xyz";
+      port = 443;
+      scheme = "https";
+    }
+    {
+      hostname = "seed.radicle.garden";
+      port = 443;
+      scheme = "https";
+    }
+  ];
+}).overrideAttrs (prev: {
+  postInstall =
+    (prev.postInstall or "")
+    + ''
+      ln -s ${./youthlic-seed-header.png} $out/images/youthlic-seed-header.png
+      ln -s ${./youthlic-seed-avatar.jpg} $out/images/youthlic-seed-avatar.jpg
+    '';
+})