Add sli.do short link redirect (#4419)

Author: estyxx

frontend/next.config.js

@@ -76,6 +76,11 @@ const nextConfig = {
         destination: "https://discord.gg/dWDVQJMfYW",
         permanent: false,
       },
+      {
+        source: "/slido",
+        destination: "https://app.sli.do/event/x8n8psMWm7xZwtmzJ49KKh",
+        permanent: false,
+      },
       {
         source: "/blog",
         destination: "/news",