;doc: csv: note a limitation with datetimes in other zones

hledger/hledger.m4.md

@@ -3865,6 +3865,11 @@ date-format %-m/%-d/%Y %l:%M %p some other junk
 For the supported strptime syntax, see:\
 <https://hackage.haskell.org/package/time/docs/Data-Time-Format.html#v:formatTime>
 
+Note that although you can parse date-times which include a time zone, 
+that time zone is ignored; it will not change the date that is parsed.
+This means when reading CSV data with times not in your local time zone,
+dates can be "off by one".
+
 
 ### `decimal-mark`