Usage Ping - Add firewall exception info to docs

doc/development/product_analytics/usage_ping.md

@@ -117,7 +117,10 @@ sequenceDiagram
 1. When the cron job runs, it calls [`GitLab::UsageData.to_json`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/services/submit_usage_ping_service.rb#L22).
 1. `GitLab::UsageData.to_json` [cascades down](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/usage_data.rb#L22) to ~400+ other counter method calls.
 1. The response of all methods calls are [merged together](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/usage_data.rb#L14) into a single JSON payload in `GitLab::UsageData.to_json`.
-1. The JSON payload is then [posted to the Versions application]( https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/services/submit_usage_ping_service.rb#L20).
+1. The JSON payload is then [posted to the Versions application]( https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/services/submit_usage_ping_service.rb#L20)
+   If a firewall exception is needed, the required URL depends on several things. If 
+   the hostname is `version.gitlab.com`, the protocol is `TCP`, and the port number is `443`,
+   the required URL is <https://version.gitlab.com/>.
 
 ## Implementing Usage Ping