Add reference about relative dates to Query Builder POD

Add reference about DateTime::Format::Natural to Query Builder POD
with a few examples.

docs/query_builder.pod

@@ -512,6 +512,24 @@ To compare LargeContent instead:
 
     CF.IP = CF.IPRange.LargeContent
 
+=item Search tickets by relative dates
+
+RT supports relative dates in searches, so you can search for tickets
+that were resolved in the last week, during the last month, as well as
+other relative dates.
+
+For example, if you want to search tickets created during the last month,
+you can use the following search:
+
+    Created >= 'beginning of last month' and Created < 'this month'
+
+Or if you want to search tickets resolved since the last week:
+
+    Resolved >= 'last week'
+
+You can check relative date strings that RT supports at
+L<https://metacpan.org/pod/DateTime::Format::Natural::Lang::EN> .
+
 =back
 
 =head1 Learn More