improve documentation about timestamp format

Author: David Bariod

json_formatter.go

@@ -23,6 +23,9 @@ func (f FieldMap) resolve(key fieldKey) string {
 // JSONFormatter formats logs into parsable json
 type JSONFormatter struct {
 	// TimestampFormat sets the format used for marshaling timestamps.
+	// The format to use is the same than for time.Format or time.Parse from the standard
+	// library.
+	// The standard Library already provides a set of predefined format.
 	TimestampFormat string
 
 	// DisableTimestamp allows disabling automatic timestamps in output

text_formatter.go

@@ -53,7 +53,10 @@ type TextFormatter struct {
 	// the time passed since beginning of execution.
 	FullTimestamp bool
 
-	// TimestampFormat to use for display when a full timestamp is printed
+	// TimestampFormat to use for display when a full timestamp is printed.
+	// The format to use is the same than for time.Format or time.Parse from the standard
+	// library.
+	// The standard Library already provides a set of predefined format.
 	TimestampFormat string
 
 	// The fields are sorted by default for a consistent output. For applications