clarify best way to install custom CA

doc/integration/README.md

@@ -48,7 +48,11 @@ at SuperUser also has relevant information.
 
 **Omnibus Trusted Chain**
 
-It is enough to concatenate the certificate to the main trusted certificate:
+[Install the self signed certificate or custom certificate authorities](http://docs.gitlab.com/omnibus/common_installation_problems/README.html#using-self-signed-certificate-or-custom-certificate-authorities)
+in to GitLab Omnibus.
+
+It is enough to concatenate the certificate to the main trusted certificate
+however it may be overwritten during upgrades:
 
 ```bash
 cat jira.pem >> /opt/gitlab/embedded/ssl/certs/cacert.pem