README: add IP fallback, dd safety note, and Arch build-deps command

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -36,6 +36,7 @@ Arch Linux server**:
 ## Requirements (on the build machine)
 
 - A Linux box with: `xorriso`, `squashfs-tools`, `git`, `sha512sum`, `sudo`.
+  On Arch: `sudo pacman -S libisoburn squashfs-tools git coreutils`.
 - A **stock Arch ISO** (filename starting with `archlinux-`) from
   <https://archlinux.org/download/>, placed next to the script.
 - An SSH public key (used for the headless server's only login method).
@@ -67,6 +68,8 @@ or write it to a stick directly:
 sudo dd if=omalocal-arch-YYYYMMDD.iso of=/dev/sdX bs=4M status=progress conv=fsync
 ```
 
+Find the stick with `lsblk` first — `dd` to the wrong device will erase it.
+
 Boot the target in **UEFI** mode. The installer auto-starts on the console:
 it brings up networking (wired or Wi-Fi), prompts for hostname / user / password
 / target disk (with a type-to-confirm guard before it wipes anything), installs
@@ -80,6 +83,9 @@ SSH in with the key you baked in:
 ssh <user>@<hostname>.local
 ```
 
+(If `.local` doesn't resolve from your client, use the server's IP — it's shown
+on the server's console login screen.)
+
 You'll be asked once whether to set the server up. Saying yes installs **Once**,
 optionally **Omarchy-Send**, then **OMATERM**, and leaves you in tmux.