Add CNAME entry for portal.sleepover (#2820)

Portal website for the sleepover athena event happening this week

Author: celesteroselli

hackclub.com.yaml

@@ -4986,6 +4986,13 @@ slashz:
   type: CNAME
   value: a.selfhosted.hackclub.com.
 sleepover: #celeste@hackclub.com @thegrammarpolice
+- octodns:
+    cloudflare:
+      proxied: true
+  ttl: 300
+  type: CNAME
+  value: a.selfhosted.hackclub.com.
+portal.sleepover: #celeste@hackclub.com @thegrammarpolice
 - octodns:
     cloudflare:
       proxied: true