Revert "remove apex domain docs: add back when released"

This reverts commit 386a9ca.

docs/_docs/routing/custom-domain.md

@@ -88,6 +88,21 @@ Jets.application.configure do
   config.domain.route53 = false # disable route53 from being managed by jets.
 ```
 
+## Route53 Apex Domain
+
+Jets creates a CNAME route53 record by default. Jets can also create zone apex records or naked domain names. Example:
+
+```ruby
+Jets.application.configure do
+  config.domain.cert_arn = "arn:aws:acm:us-west-2:112233445577:certificate/8d8919ce-a710-4050-976b-b33da991e7e8" # String
+  config.domain.hosted_zone_name = "coolapp.com" # String
+  config.domain.name = "coolapp.com"
+  config.domain.apex = true # # apex or naked domain. Use AliasTarget with an A record instead of a CNAME
+end
+```
+
+Though apex records are supported, it is recommended to put CloudFront of the API Gateway Custom Domain instead.
+
 ## CloudFront Recommendation
 
 For the most control, it is recommended to create a CloudFront distribution **outside** of Jets. Then put CloudFront in front of the API Gateway Custom Domain.  Example: