BookStack is a great little wiki that uses bookcases and books to organize documentation. This is how it was installed on a Raspberry Pi4 running Ubuntu Server 20.04.
The official documentation for BookStack can be found HERE
Go to the /tmp directory:
cd /tmp


Download the script:
wget https://raw.githubusercontent.com/BookStackApp/devops/master/scripts/installation-ubuntu-20.04.sh


Make the script executable:
sudo chmod a+x installation-ubuntu-20.04.sh


Install Bookstack on Ubuntu 20.04:
Run the script:
sudo ./installation-ubuntu-20.04.sh

Add the url of the site when prompted:


Press Enter to continue the install.

After about 5 minutes BookStack will be installed:

In a browser type the ip address or url and this will open the logon page:

Log in using the default user of admin@admin.com and the default password of password.

Bookstack is now ready to setup.