Add cross-machine setup guide

docs/SETUP_ON_NEW_MACHINE.md

@@ -0,0 +1,57 @@
+# Continuing on another machine
+
+This project is a self-contained git repo. Everything needed to build and run is
+in it except **Godot itself** (which you install once per machine). No assets to
+download — the M0 world is generated in code.
+
+## 1. Install Godot 4.3+
+- **macOS / Windows / Linux:** download the *standard* build (NOT the .NET/C#
+  build — this project is pure GDScript) from https://godotengine.org/download
+- Any 4.3.x or newer 4.x works. The project was built on `4.3.stable`.
+
+## 2. Get the project onto the machine
+You have the folder (from the zip, or a git remote). Then:
+
+```bash
+# If you brought the .zip:
+unzip valheimlike.zip
+cd valheimlike
+
+# If you use a git remote instead (recommended for ongoing work):
+git clone <your-remote-url> valheimlike
+cd valheimlike
+```
+
+## 3. Open / run it
+```bash
+# Open in the editor (first open rebuilds the local .godot cache — this is normal):
+godot --path .            # or: open Godot, "Import", pick this folder's project.godot
+
+# Run the game directly:
+godot --path .
+```
+On macOS the binary inside the app is:
+`/Applications/Godot.app/Contents/MacOS/Godot --path .`
+
+## Controls
+WASD move · Mouse look · Shift sprint · Space jump · ESC frees the cursor.
+
+## Notes
+- The `.godot/` cache folder is machine-local and git-ignored — it regenerates on
+  first open. Don't copy it between machines.
+- If scripts look like they "didn't load", let the first editor open finish its
+  import pass, then press play.
+- Where we are: **M0 complete** (walkable lit world). Next is **M1** (gather →
+  craft → build). See `docs/ROADMAP.md`.
+
+## Recommended: push to a git remote for cross-machine work
+A zip is a one-time snapshot. For going back and forth between machines, create a
+private remote once and push:
+
+```bash
+# GitHub (private):  gh repo create valheimlike --private --source=. --push
+# or any remote:
+git remote add origin <your-remote-url>
+git push -u origin main   # (branch may be 'master' — check `git branch`)
+```
+Then on each machine it's just `git clone` / `git pull` / `git push`.