fix sitemap

src/public/robots.txt

@@ -0,0 +1,3 @@
+User-agent: *
+
+Sitemap: /sitemap.php

src/public/sitemap.php

@@ -0,0 +1,25 @@
+<?php
+
+header('Content-type: application/xml; charset=utf-8');
+
+echo '<?xml version="1.0" encoding="UTF-8"?>';
+echo '<urlset>';
+
+if ($signals = file_get_contents(__DIR__ . '/../../SIGNALS/YGGDRASIL.md')) {
+
+  foreach (explode(PHP_EOL, $signals) as $signal) {
+
+    if (preg_match('/\[(.*?)\]\((.*?)\)/ui', $signal, $data)) {
+
+      if (!empty($data[1]) && !empty($data[2])) {
+
+        if ($host = parse_url($data[2], PHP_URL_HOST)) {
+
+          echo sprintf('<url><loc>%s</loc></url>', htmlentities($data[2]));
+        }
+      }
+    }
+  }
+}
+
+echo '</urlset>';