How to download and setup psi
Open terminal and run command
                                            git clone https://github.com/komninoschat/psi.git
                                        
                                        git clone is used to create a copy or clone of psi repositories.
                                        You pass git clone a repository URL. it supports a few different network protocols and corresponding URL formats.
Also you may download zip file with psi https://github.com/komninoschat/psi/archive/master.zip
Or simply clone psi with SSH
                                            [email protected]:komninoschat/psi.git