adds .perl refs #2632

Added the fact that from version 6.2, .perl can be called on Date

doc/Type/Date.pod6

@@ -27,6 +27,8 @@ an object the current day according to the system clock.
     my $n = Date.new('2015-12-31'); # New Year's Eve
     say $n - $d;                    # OUTPUT: «7␤», 7 days between New Years/Christmas Eve
     say $n + 1;                     # OUTPUT: «2016-01-01␤»
+    
+B<Note> since version 6.2, .perl can be called on C<Date>.
 
 =head1 Methods
 
@@ -361,4 +363,4 @@ L«C<Date>|/type/Date» object.
 
 =end pod
 
-# vim: expandtab softtabstop=4 shiftwidth=4 ft=perl6
+# vim: expandtab softtabstop=4 shiftwidth=4 ft=perl6