add "Concurrent builds are counted per account." (#17564)

add "Concurrent builds are counted per account."

Author: kbitr

src/content/docs/pages/platform/limits.mdx

@@ -16,7 +16,7 @@ Below are limits observed by the Cloudflare Free plan. For more details on remov
 
 Each time you push new code to your Git repository, Pages will build and deploy your site. You can build up to 500 times per month on the Free plan. Refer to the Pro and Business plans in [Pricing](https://pages.cloudflare.com/#pricing) if you need more builds.
 
-Builds will timeout after 20 minutes.
+Builds will timeout after 20 minutes. Concurrent builds are counted per account.
 
 ## Custom domains