docs(nix/tag): fix example for discrDef

Change-Id: I8b7accb399448f57ace502642bd91fcfae416f15
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3507
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>

nix/tag/default.nix

@@ -43,8 +43,8 @@ let
   #   discrDef "smol" [
   #     { biggerFive = i: i > 5; }
   #     { negative = i: i < 0; }
-  #   ] -100
-  #   => { negative = 100; }
+  #   ] (-100)
+  #   => { negative = -100; }
   #   discrDef "smol" [
   #     { biggerFive = i: i > 5; }
   #     { negative = i: i < 0; }