TUIs are now optional if not set

Change-Id: I01b552bb37012c8a0b69a527667173c22ff5e1fb
diff --git a/script/korapxml2krill b/script/korapxml2krill
index 16d80d5..f534185 100644
--- a/script/korapxml2krill
+++ b/script/korapxml2krill
@@ -14,6 +14,7 @@
 use KorAP::XML::Archive;
 use KorAP::XML::Tokenizer;
 use Parallel::ForkManager;
+# TODO: use Parallel::Loops
 
 # CHANGES:
 # ----------------------------------------------------------