Added "Supported Distributions" section

The new section contains RHEL/CentOS 7.4+ and Fedora26+ for now.

README.md

@@ -4,10 +4,14 @@ This repository contains [Ansible](https://www.ansible.com/) roles and playbooks
 
 **Note**: The ansible playbooks and roles require a configured ansible environment where the ansible nodes are reachable and are properly set up to have an IP address and a working package manager.
 
-**Supported FreeIPA versions**
+## Supported FreeIPA versions
 
 For now only FreeIPA versions 4.5 and up are supported. The client role should also be functional with FreeIPA 4.4.
 
+## Supported Distributions
+* RHEL/CentOS 7.4+
+* Fedora 26+
+
 ## Roles
 
 [Client](CLIENT.md)