Add known issues documentation for speedy routing

docs/known_issues.md

@@ -0,0 +1,31 @@
+---
+
+## Known Issues
+
+### Speedy IsoBased Routing with Test Data
+
+When using the `speedy_isobased` algorithm with the provided
+test weather and depth datasets, routing may terminate early
+with the error:
+
+> All pruning segments fully constrained
+
+#### Symptoms
+- Routing stops after ~10–11 isochrone steps
+- No runtime exception occurs
+- No route reaches the destination
+- A partial route file is generated with 0% success
+
+#### Cause (Observed)
+This occurs when all isochrone pruning segments become constrained
+due to the interaction of:
+- Pruning parameters
+- Environmental constraints (land, depth, map bounds)
+- Test data resolution
+
+#### Suggested Workarounds
+Users may try:
+- Increasing `ISOCHRONE_PRUNE_SEGMENTS`
+- Reducing `ISOCHRONE_PRUNE_SECTOR_DEG_HALF`
+- Increasing heading resolution
+- Reducing pruning strictness