#in Debian 9, first add the third party Neofetch repository as shown
echo "deb http://dl.bintray.com/dawidd6/neofetch jessie main" | sudo tee -a /etc/apt/sources.list
#next, append the Neofetch key using the command as shown below
curl -L "https://bintray.com/user/downloadSubjectPublicKey?username=bintray" -o Release-neofetch.key && sudo apt-key add Release-neofetch.key && rm Release-neofetch.key
#Update the sources list by updating the system using the command below
apt-get update
#Finally, install Neofetch
apt-get install neofetch
#To launch Neofetch, run
neofetch