correct tm_year representation; include comments from `man 2 tm`

Src/pcf8523.c

@@ -109,13 +109,15 @@ time_t pcf8523_now(pcf8523_t *pcf8523)
 
 	/* read current time */
 	pcf8253_read(pcf8523, PCF_REG_SECONDS, buf, 7);
-	t.tm_sec  = bcd2bin(buf[0]);
-	t.tm_min  = bcd2bin(buf[1]);
-	t.tm_hour = bcd2bin(buf[2]);
-	t.tm_mday = bcd2bin(buf[3]);
-	t.tm_wday = bcd2bin(buf[4]); /* ignored by mktime */
-	t.tm_mon  = bcd2bin(buf[5]);
-	t.tm_year = bcd2bin(buf[6]) + 2000;
+	t.tm_sec  = bcd2bin(buf[0]);       /* Seconds          [0, 60] */
+	t.tm_min  = bcd2bin(buf[1]);       /* Minutes          [0, 59] */
+	t.tm_hour = bcd2bin(buf[2]);       /* Hour             [0, 23] */
+	t.tm_mday = bcd2bin(buf[3]);       /* Day of the month [1, 31] */
+	t.tm_wday = bcd2bin(buf[4]);       /* Month            [0, 11]  (January = 0) */
+	t.tm_yday = 0;                     /* Day of the year  [0, 365] (Jan/01 = 0) */
+	t.tm_mon  = bcd2bin(buf[5]);       /* Month            [0, 11]  (January = 0) */
+	t.tm_year = bcd2bin(buf[6]) + 100; /* Year minus 1900 */
+	/* tm_wday and tm_yday are ignored by mktime() */
 	time = mktime(&t);
 
 	return time;