docs: add GPS alternative and pathfinding usage to quickstart guide

QUICKSTART.md

@@ -64,6 +64,36 @@ You should see:
 **GPS not working?**
 - Set up 4 GPS host computers at high altitude
 - Run `gps host X Y Z` on each (with their coordinates)
+- **Alternative:** If running Opus OS, use its `gpsServer` package — a single
+  turtle can self-build a complete GPS constellation (replaces 4 host computers)
+
+## Pathfinding
+
+The turtle now includes a built-in pathfinding module exposed as `_G._pathfind`.
+You can trigger it from the web UI via eval commands:
+
+```lua
+-- Navigate to coordinates (avoids obstacles)
+_pathfind.goto(100, 65, -200)
+
+-- Navigate with block digging enabled
+_pathfind.goto(100, 65, -200, { dig = true })
+
+-- Go home
+_pathfind.goHome()
+
+-- Face a specific heading (0=south, 1=west, 2=north, 3=east)
+_pathfind.face(3)
+
+-- Get current heading name
+_pathfind.headingName()  -- "east"
+```
+
+The pathfinder:
+- Uses GPS for initial position, then tracks movement locally
+- Auto-detects heading on startup via GPS triangulation
+- Handles obstacles by trying to go over/around them
+- Supports optional block digging for clearing paths
 
 ## Next Steps