Merge pull request rails#45811 from augustocbx/improve_conf-hosts_documentation

Update docs for `conf.hosts` to be more explicit about the main domain

Author: rafaelfranca

guides/source/configuring.md

@@ -755,11 +755,10 @@ The provided regexp will be wrapped with both anchors (`\A` and `\z`) so it
 must match the entire hostname. `/product.com/`, for example, once anchored,
 would fail to match `www.product.com`.
 
-A special case is supported that allows you to permit all sub-domains:
+A special case is supported that allows you to permit the domain and all sub-domains:
 
 ```ruby
-# Allow requests from subdomains like `www.product.com` and
-# `beta1.product.com`.
+# Allow requests from the domain itself `product.com` and subdomains like `www.product.com` and `beta1.product.com`.
 Rails.application.config.hosts << ".product.com"
 ```