Add firewalld dep (not default on CentOS cloud images)

doc/install.md

@@ -12,7 +12,7 @@ The current version of SOCTools only runs on a single server. A fully distribute
 * Minimal installation of CentOS7
 * Install Ansible
   * `sudo yum -y install epel-release`  
-  * `sudo yum -y install ansible git`
+  * `sudo yum -y install ansible git firewalld`
   * `sudo ansible-galaxy collection install ansible.posix`
 
 ## Clone SOCTools