feat: update readmes and keys and fixes

pi/README.md

@@ -16,6 +16,14 @@ On startup it also syncs the initial state.
 
 ## Setup
 
+### Prerequisites
+
+If you're building on an x86_64 machine, you need binfmt emulation for aarch64. On NixOS, add this to your system config and rebuild:
+
+```nix
+boot.binfmt.emulatedSystems = [ "aarch64-linux" ];
+```
+
 ### 1. Flash the SD card
 
 ```sh
@@ -23,14 +31,12 @@ nix build .#nixosConfigurations.bootstrap.config.system.build.sdImage
 dd if=result/sd-image/*.img of=/dev/sdX bs=4M status=progress
 ```
 
-Boot the Pi. It connects to the Noisebridge WiFi automatically.
+Boot the Pi. It connects to the Noisebridge WiFi automatically and is discoverable via mDNS as `noisebridge-pi.local`.
 
 ### 2. Find the Pi
 
 ```sh
-nmap -sn 192.168.1.0/24
-# or
-arp -a
+ping noisebridge-pi.local
 ```
 
 ### 3. SSH host key
@@ -38,7 +44,7 @@ arp -a
 Grab the key and add it to `secrets/secrets.nix`:
 
 ```sh
-ssh-keyscan <pi-ip> | grep ed25519
+ssh-keyscan noisebridge-pi.local 2>/dev/null | grep ed25519
 ```
 
 ```nix