Added some more details to README file

README.md

@@ -3,12 +3,15 @@ Read Me
 
 1. About
 
-These Ansible roles allow you to install, from a deployment host, iRODS [4.2.0 - 4.2.8] on one or more CentOS 7.x x86_64 hosts. The iRODS role is compatible with both provider and consumer installation modes. PostgreSQL (from 9.4 to 13 on CentOS 7.x or 10.6 on CentOS 8.x) will be used to serve the iCAT catalogue. All firewalls should be stopped before attempting a deployment.
+These Ansible roles allow you to install, from a deployment host, iRODS [4.2.0 - 4.2.8] on one or more CentOS 7.x x86_64 hosts. The iRODS role is compatible with both provider and consumer installation modes. PostgreSQL (stock versions from the distribution or newer ones) will be used to serve the iCAT catalogue. All firewalls should be stopped before attempting a deployment.
 
 2. Ansible installation 
 
 ```bash
+yum install epel-release # as root
+yum update # as root
 yum install python2-pip # as root
+pip install --upgrade pip # as root
 pip install ansible --user # first installation
 pip install -U ansible --user # update
 ```
@@ -25,6 +28,7 @@ This Gitlab repository is comprised of two Ansible roles:
 4. Fetch the roles
 
 ```bash
+yum install git # as root
 mkdir -p ansible/{group_vars/{iRODS,all},host_vars,roles} ; cd ansible
 $ git clone https://dci-gitlab.cines.fr/poc_irods/poc-irods.git roles
 ```