Clarify Julian Date reference

lib/Neo4j/Types/DateTime.pod

@@ -70,10 +70,9 @@ L<Neo4j::Types::DateTime> specifies the following methods.
 Return the number of full days since the Unix epoch.
 For C<* TIME> values, return C<undef>.
 
-In reference to the
+For the day identified by C<$days>, the
 L<Julian Date|https://en.wikipedia.org/wiki/Julian_date>
-C<$jd>, the day identified by C<$days> begins exactly
-at C<$jd - 2440587.5>.
+is exactly C<$days + 2440587.5>.
 
 =head2 epoch