Add Pearkin Attack Server to server.json

We're a new community starting out with Mindustry.
Its a chill and relax attack server with RTV, stats, and Discord moderation setup.

servers.json

@@ -73,5 +73,8 @@
   },
   {
     "address": "pandorum.su:9999"
+  },
+  {
+    "address": "attack.pearkin.net"
   }
 ]