fix index entry for use lib

Author: gfldex

doc/Language/modules.pod6

@@ -337,7 +337,7 @@ Then use the tag you like and pick the symbol by its name.
 
 =head2 Finding Modules
 
-X<use lib>
+X<|use lib>
 A user may have a collection of modules not found in the normal ecosystem,
 maintained by a module or package manager, but needed regularly.  Instead of
 using the C<use lib> pragma one can use the C<PERL6LIB> environment variable to