Add documentation about the ".min.css" suffix

Author: smnandre

ux.symfony.com/assets/styles/demos/live-memory.min.css

@@ -1,5 +1,9 @@
 /** -----------------------------------------------------------------
  * LiveMemory demo
+ *
+ * This file is suffixed with `.min.css` to prevent it from being
+ * processed by the CDN compression system, which would break the
+ * most recent CSS syntax (as layers) used in this file.
  * --------------------------------------------------------------- */
 
 @import "live-memory/app/reset";