Add warning value for initial layer line width

150% seems about right. Then you get a warning value for lines thicker than 0.525mm on a 0.4mm nozzle.

resources/definitions/fdmprinter.def.json

@@ -833,6 +833,7 @@
                             "unit": "%",
                             "default_value": 100.0,
                             "minimum_value": "0.001",
+                            "maximum_value_warning": "150",
                             "settable_per_mesh": false,
                             "settable_per_extruder": true
                         }