Update klogrus.go

Improve existing documentation

plugin/klogrus/klogrus.go

@@ -13,6 +13,8 @@ var (
 )
 
 // FieldLogger interface.
+// combines logrus.FieldLogger with GetLevel method
+// useful to represent a wrapper around *logrus.Logger
 type FieldLogger interface {
 	logrus.FieldLogger
 	GetLevel() logrus.Level
@@ -30,6 +32,9 @@ func New(lr *logrus.Logger) *Logger {
 }
 
 // NewFieldLogger returns a new Logger using a FieldLogger interface.
+// it is isofunctional with New constructor, except it can accept either
+// *logrus.Logger or a possible wrapper thaf implements logrus.FieldLogger
+// and includes GetLevel method.
 func NewFieldLogger(fl FieldLogger) *Logger {
 	return &Logger{fl}
 }