Document new option

text_formatter.go

@@ -34,6 +34,8 @@ type TextFormatter struct {
 	// Set to true to bypass checking for a TTY before outputting colors.
 	ForceColors   bool
 	DisableColors bool
+	// Set to true to disable timestamp logging (useful when the output
+	// is redirected to a logging system already adding a timestamp)
 	DisableTimestamp bool
 }