standardize link

Author: coke

doc/Language/variables.rakudoc

@@ -1504,7 +1504,7 @@ when provided with the relative path from the distribution's top-level
 directory.
 
 C<$?DISTRIBUTION> only returns information when used inside a module. In scripts
-it contains C<Nil>.
+it contains L<C<Nil>|/type/Nil>.
 
 =begin code
 sub module-source {