[Rules] Update troubleshooting.mdx (cloudflare#23029)

Author: cf-scott

src/content/docs/rules/custom-errors/troubleshooting.mdx

@@ -35,7 +35,7 @@ You cannot customize the following 1XXX errors via Error Pages:
 
 ## Custom error page size
 
-Your custom error page cannot be blank and cannot exceed 1.5 MB in size (1,500,000 characters). To avoid exceeding the custom error page limit, preview your page to check its size before publishing.
+Your custom error page cannot be blank and the combined size of all page assets cannot exceed 1.5 MB (1,500,000 characters). To avoid exceeding the custom error page limit, preview your page to check its size before publishing.
 
 ## General troubleshooting advice