Make it explicit where is the gitlab.rb file

Save people an extra Google search if this is the
first doc they're reading.

doc/administration/auth/how_to_configure_ldap_gitlab_ce/index.md

@@ -107,7 +107,7 @@ Global Admins     GitLab.org/GitLab INT/Global Groups/Global Admins
 
 ## GitLab LDAP configuration
 
-The initial configuration of LDAP in GitLab requires changes to the `gitlab.rb` configuration file. Below is an example of a complete configuration using an Active Directory.
+The initial configuration of LDAP in GitLab requires changes to the `gitlab.rb` configuration file (`/etc/gitlab/gitlab.rb`). Below is an example of a complete configuration using an Active Directory.
 
 The two Active Directory specific values are `active_directory: true` and `uid: 'sAMAccountName'`. `sAMAccountName` is an attribute returned by Active Directory used for GitLab usernames. See the example output from `ldapsearch` for a full list of attributes a "person" object (user) has in **AD** - [`ldapsearch` example](#using-ldapsearch-unix)