xref to env vars

Author: tbrowder

doc/Programs/01-debugging.pod6

@@ -19,6 +19,10 @@ Please see the documentation for these programs for further information.
 Historically others have existed and others are likely to be written in the future,
 check the L<Perl 6 Modules|https://modules.perl6.org/> website.
 
+There are also environment variables that can be set to aid debugging various aspects
+of your program.  See L<Perl 6 Environment Variables|https://docs.perl6.org/programs/running>
+for more information.
+
 =head2 C<trace> pragma
 
 The C<trace> pragma causes the program to print out step-by-step which lines