Update hardpoint_design.md

Adding cabin person capacities

design-document/hardpoint_design.md

@@ -110,11 +110,11 @@ Cabins are a special-case equipment item, consuming no "equipment space" volume
 
 The actual dimensions of a cabin slot may vary from ship to ship, but the volume allocated to a cabin slot should be approximately the same across all slots of the same size:
 
-- **S1**: 12.5m³
-- **S2**: 40.0m³
-- **S3**: 128m³
-- **S4**: 410m³
-- **S5**: 1320m³
+- **S1**: 12.5m³ - 1 person
+- **S2**: 40.0m³ - 3 people
+- **S3**: 128m³ - 8 people
+- **S4**: 410m³ - 22 people
+- **S5**: 1320m³ - 60 people
 
 ## Hull Variants