add ip addreses info.

README.md

@@ -6,6 +6,7 @@
 - [How do I get help?](#how-do-i-get-help)
 - [What is the minimum setup before I start using GitLab?](#what-is-the-minimum-setup-before-i-start-using-gitlab)
 - [What are GitLab usage limits?](#what-are-gitlab-usage-limits)
+- [What are the IP addresses I should whitelist if I run services behind firewall?](#what-are-the-ip-addresses-i-should-whitelist-if-i-run-services-behind-firewall)
 - [How to generate and upload GitLab ssh-key?](#how-to-generate-and-upload-gitlab-ssh-key)
 - [What is a GitLab project?](#what-is-a-gitlab-project)
 - [What is the username space?](#what-is-the-username-space)