Add required packages

diff --git a/doc/plugins/contrib/datetime_cmp.mdwn b/doc/plugins/contrib/datetime_cmp.mdwn
index ba35b37c60b23363e20890630d2b7376f4d8fef1..47eaffaec0cc36c5c85bcda1109c5a6a6c436c80 100644 (file)
--- a/doc/plugins/contrib/datetime_cmp.mdwn
+++ b/doc/plugins/contrib/datetime_cmp.mdwn
@@ -11,6 +11,8 @@ creation or modification times.
 It also sets the date of the next modification of the page on relevant date, so
 that the page will be rebuilt if the condition changes.
 
+It requires the DateTime::Format::Duration perl module (on Debian : ``apt-get install libdatetime-format-duration-perl``).
+
 ## List of functions
 
 The list of functions is given by the following regexp: