add riddle.com to self_service_creation_platform_domains.txt (#573)

Co-authored-by: Sorted Order Validation <hello@sublimesecurity.com>

Author: zoomequipd

self_service_creation_platform_domains.txt

@@ -22,6 +22,7 @@ mockflow.com
 padlet.com
 powr.io
 publuu.com
+riddle.com
 seesaw.me
 soloist.ai
 surveymonkey.com