hide label of submethod entry

Author: Marc Chantreux

doc/Language/classtut.pod6

@@ -36,7 +36,7 @@ In the two classes, the default constructor is being used. This
 constructor will use named parameters in its invocation: C«Point.new(x =>
 0, y => 0)».
 
-X<submethods>
+X<|Submethod>
 You can also provide your own construction and C<BUILD>
 implementation.  The following, more elaborate example shows how a
 dependency handler might look in Perl 6.  It showcases custom