Add demo session

This demo session show how to install pi and install a Pharo package from CLI

Author: Hernán Morales Durand

README.md

@@ -5,6 +5,7 @@
 # Table of Contents
 
 - [Description](#description)
+- [Demo](#demo)
 - [Requirements](#requirements)
 - [Installation](#installation)
   - [Bash users](#bash-users)
@@ -28,6 +29,10 @@ PI turns copy & paste [Metacello](https://github.com/Metacello/metacello) instal
 
 PI automatically retrieves and parses Pharo GitHub repository information, and also downloads the latest stable Pharo image and virtual machine if none is found in the current directory. It also supports installing multiple packages at once.
 
+# Demo
+
+![pi-session](https://user-images.githubusercontent.com/4825959/173497407-e99cad9f-38ae-4b34-8615-92dbbad7a225.gif)
+
 # Requirements
 
   - bash or zsh