zischr is a self-service point-of-sale & accounting solution for groups of 15-20 people.
(This assumes the Pi has the single purpose of running zischr. Otherwise, you should consider a better isolation strategy. We're happy about a PR with scripts / Dockerfiles / whatever for the deployment/ directory).
Install Raspbian Stretch on your Raspberry Pi 3 (Official Guide).
Change the password of the default pi.
Afterwards, run the following commands as root:
apt-get install git
cd /root
git clone https://github.com/hadiko-i6/zischr.git /root/zischrdb_checkout
mkdir /root/zischrdb
/root/zischrdb_checkout/deployment/raspi3/deploy.sh
This installs build & runtime dependencies and deploys a copy of the relvant runtime files ot /zischr.
deploy.sh also removes everythin in /zischr (the fsdb is kept in /root/zischrdb, no worries).
To keep a Git history of zischrdb, take a look into the hook functionality of the backend server command in the zischr-backend.service file.
cd /root/zischrdb_checkout
git pull --ff-only
deployment/raspi3/deploy.sh