add ref comment

apps/app/src/components/LoadingSpinner.module.scss

@@ -2,7 +2,7 @@
   animation: animation-rotate 750ms infinite linear;
 }
 
-
+// refs: https://github.com/weseek/growi/blob/master/apps/app/src/styles/atoms/_spinners.scss
 @keyframes animation-rotate {
   100% {
     transform: rotate(360deg);