add a README

README.md

+# Chaos Parcel Serivce: Backend
+
+## Deployment
+This assumes you run the code as user *www-data*  
+Do **not** checkout this code as the same user.  
+checkout the code (main branch for production)  
+cd into the directory  
+
+```
+mkdir instance
+chown www-data:www-data instance
+```
+
+create a file .env with content
+```
+# the database location relative to the repository root
+database_url = "sqlite:///instance/paketshop.db"
+# the url for the customer frontend (the people sending parcels)
+customer_url = "https://bgp.events.ccc.de"
+# the url this app will be run under
+backend_url = "https://backend.bgp.events.ccc.de"
+# the url for the people handling the parcels
+worker_url = "https://intern.bgp.events.ccc.de"
+# a shared secret for the workers
+shared_secret = "{{ bgp_secrets.shared_secret }}"
+# a deployment wide secret key. 
+# can be created with:
+# python3 -c 'import os; print(os.urandom(16).hex())'
+signing_key = "{{ bgp_secrets.signing_key }}"
+# how long workers are logged in.
+token_lifetime = "180"
+```
+
+create a venv and install requirements:
+```
+python -m venv venv
+. venv/bin/activate
+pip install -r requirements.txt
+```
+
+We suggest to use gunicorn to server the python app, so install it
+```
+pip install gunicorn
+```
+
+create a runtime directory to allow the webserver to forward calls to
+```
+mdkir /run/bgp
+chown www-data:www-data /run/bgp
+```
+
+create a systemd service file to serve the app:
+```
+[Unit]
+Description=Gunicorn instance to serve bgp backend fastapi app
+After=network.target
+
+[Service]
+User=www-data
+Group=www-data
+WorkingDirectory=/srv/backend
+ExecStart=/srv/backend/venv/bin/gunicorn -k uvicorn.workers.UvicornWorker --bind unix:/run/bgp/socket backend.main:app
+
+[Install]
+WantedBy=multi-user.target
+```