offlineimap.conf: document the "utime_from_header" option

This was introduced in 3bc66c0858 and never
documented.

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap.conf

@@ -458,6 +458,22 @@ localfolders = ~/Test
 #restoreatime = no
 
 
+# This option stands in the [Repository LocalExample] section.
+#
+# Set modification time of messages basing on the message's "Date" header. This
+# option makes sense for the Maildir type, only.
+#
+# This is useful if you are doing some processing/finding on your Maildir (for
+# example, finding messages older than 3 months), without parsing each
+# file/message content.
+#
+# If enabled, this forbid the -q (quick mode) CLI option to work correctly.
+#
+# Default: no.
+#
+#utime_from_header = no
+
+
 [Repository GmailLocalExample]
 
 # This type of repository enables syncing of Gmail. All Maildir