Docs: Gitaly cannot mix local and remote gitaly servers

Example of the proper configuration that needs to be used
in case GitLab uses mix of local and remove Gitaly servers.

Closes: https://gitlab.com/gitlab-org/gitaly/-/issues/2183

doc/administration/gitaly/index.md

@@ -402,6 +402,17 @@ git_data_dirs({
 })
 ```
 
+You should use configuration similar to the following:
+
+```ruby
+git_data_dirs({
+  'default' => { 'gitaly_address' => 'tcp://gitaly1.internal:8075' },
+  # this should be the IP address of the GitLab server that has Gitaly running on it
+  'storage1' => { 'gitaly_address' => 'tcp://gitlab.internal:8075' },
+  'storage2' => { 'gitaly_address' => 'tcp://gitaly2.internal:8075' },
+})
+```
+
 **For Omnibus GitLab**
 
 1. Edit `/etc/gitlab/gitlab.rb`: