Add setup docs

setup.md

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+# Pi setup
+
+Flash an image using the [Raspberry Pi imager](https://www.raspberrypi.com/software/), I picked the Raspberry Pi OS Lite (based on debian trixie) and set up WiFi & SSH from the Customisation settings.
+
+## First commands
+
+```sh
+sudo raspi-config   # Then select: Interface Options -> SPI -> Enable
+
+sudo apt update && sudo apt upgrade
+sudo apt install -y python3-pip python3-pil python3-smbus python3-numba
+
+sudo systemctl mask swap.target
+sudo systemctl disable --now bluetooth
+sudo nmcli c modify <your-connection> 802-11-wireless.powersave 2
+```
+
+Reduce SD card writes by setting `Storage=volatile` in `/etc/systemd/journald.conf`.
+
+## Deploying
+
+Ensure [.env](src/.env) has the correct paths and then run:
+
+`./sync.sh`
+
+> That rsyncs `src/` over.
+
+## Setting up cron
+
+In `crontab -e`, add:
+
+```
+*/15 * * * * cd ~/frame && python3 display.py -o 90 >> ~/frame.log 2>&1
+```
+
+### Optionally, to monitor the wifi connection:
+
+In `sudo crontab -e`, add:
+
+```
+@reboot /usr/sbin/iw wlan0 set power_save off*/5 * * * * /home/<user>/frame/wifi-check.sh >> /home/<user>/wifi.log 2>&1
+```
+
+## Hardware notes
+
+The driver in `src/lib/waveshare_epd/` is adapted from Waveshare's [PhotoPainter](https://www.waveshare.com/wiki/PhotoPainter) project. That wikipage has the wiring, init sequence, and 6-colour palette docs.