Changes phrasing for description of binding

It limits itself to the problem pointed out in the OP, so this should
close #1378.

The terminology suggested by @smls is great, but it might be better to
open some issues to pages where it's not well expressed.

doc/Language/list.pod6

@@ -85,17 +85,19 @@ also contain these objects, but C<@>-sigiled variables always do, and
 are expected to act the part.
 
 By default, when you assign a C<List> to an C<@>-sigiled variable, you create
-an C<Array>. Those are described below. If, instead you want to put an actual
-C<List> into an C<@>-sigiled variable, you can use binding with C<:=> instead.
+an C<Array>. Those are described below. If instead you want to refer directly to a
+C<List> object using an C<@>-sigiled variable, you can use binding with C<:=> instead.
 
     my @a := 1, 2, 3;
 
 One of the ways C<@>-sigiled variables act like lists is by always supporting
 L<positional subscripting|/language/subscripts>. Anything bound to a C<@>-sigiled
-value must support the L<Positional|/type/Positional> role which guarantees this:
+value must support the L<Positional|/type/Positional> role which guarantees that this is going to fail:
 
     my @a := 1; # Type check failed in binding; expected Positional but got Int
 
+
+
 =head1 Reset a List Container
 
 To remove all elements from a Positional container assign