documentation of Eggert mods

SCCS-file: newstrftime.3
SCCS-SID: 7.12

newstrftime.3

@@ -115,6 +115,9 @@ is replaced by the day of the month as a decimal number (01-31).
 is replaced by the day of month as a decimal number (1-31);
 single digits are preceded by a blank.
 .TP
+%F
+is replaced by the date in the format %Y-%m-%d.
+.TP
 %G
 is replaced by the ISO 8601 year with century as a decimal number.
 .TP
@@ -203,6 +206,9 @@ is replaced by the year with century as a decimal number.
 %y
 is replaced by the year without century as a decimal number (00-99).
 .TP
+%z
+is replaced by the offset from UCT in the format +HHMM or -HHMM as appropriate.
+.TP
 %Z
 is replaced by the time zone name.
 .TP