Resolve "Add how to use nip.io to Auto DevOps and Kubernetes documentation"

app/views/projects/settings/ci_cd/_autodevops_form.html.haml

@@ -36,5 +36,6 @@
             = form.text_field :domain, class: 'form-control', placeholder: 'domain.com'
             .help-block
               = s_('CICD|You need to specify a domain if you want to use Auto Review Apps and Auto Deploy stages.')
+              = link_to icon('question-circle'), help_page_path('topics/autodevops/index.md', anchor: 'auto-devops-base-domain'), target: '_blank'
 
           = f.submit 'Save changes', class: "btn btn-success prepend-top-15"

doc/topics/autodevops/index.md

@@ -135,6 +135,11 @@ and `1.2.3.4` is the IP address of your load balancer; generally NGINX
 ([see prerequisites](#prerequisites)). How to set up the DNS record is beyond
 the scope of this document; you should check with your DNS provider.
 
+Alternatively you can use free public services like [xip.io](http://xip.io) or
+[nip.io](http://nip.io) which provide automatic wildcard DNS without any
+configuration. Just set the Auto DevOps base domain to `1.2.3.4.xip.io` or
+`1.2.3.4.nip.io`.
+
 Once set up, all requests will hit the load balancer, which in turn will route
 them to the Kubernetes pods that run your application(s).