Add documentation for filename_use_mail_timestamp.

Signed-off-by: Sébastien Gross <seb•ɑƬ•chezwam•ɖɵʈ•org>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap.conf

@@ -514,6 +514,29 @@ localfolders = ~/Test
 #utime_from_header = no
 
 
+# This option stands in the [Repository LocalExample] section.
+#
+# This option is similar to "utime_from_header" and could be use as a
+# complementary feature to keep track of a message date. This option only
+# makes sense for the Maildir type.
+#
+# By default each message is stored in a file which prefix is the fetch
+# timestamp and an order rank such as "1446590057_0". In a multithreading
+# environment message are fetched in a random order, then you can't trust
+# the file name to sort your boxes.
+#
+# If set to "yes" the file name prefix if build on the message "Date" header
+# (which should be present) or the "Received-date" if "Date" is not
+# found. If neither "Received-date" nor "Date" is found, the current system
+# date is used.  Now you can quickly sort your messages using their file
+# names.
+#
+# Used in combination with "utime_from_header" all your message would be in
+# order with the correct mtime attribute.
+#
+#filename_use_mail_timestamp = no
+
+
 [Repository GmailLocalExample]
 
 # This type of repository enables syncing of Gmail. All Maildir