add burner error

README.md

@@ -8,7 +8,7 @@ classDiagram
 Inputs <|-- Control
 Outputs <|-- Control
 Inputs <|-- Safety
-Outputs <|-- Safety
+Outputs <|--|> Safety
 
 Inputs <|-- HTTP_Metrics
 Outputs <|-- HTTP_Metrics
@@ -21,6 +21,7 @@ Safety <|-- HTTP_Metrics
         +getOutdoorTemperature()
         +getInletFlowTemperature()
         +getReturnFlowTemperature()
+        +getBurnerError()
     }
 
     class Outputs{