Show Associative-like access of Pair

And fix some output comment formatting.

Author: Altai-man

doc/Type/Pair.pod6

@@ -74,10 +74,10 @@ possible to change the value from outside of the C<Pair> itself:
 =begin code
 my $v = 'value A';
 my $pair = a => $v;
-$pair.say;  # OUTPUT: a => value A
+$pair.say;  # OUTPUT: «a => value A␤»
 
 $v = 'value B';
-$pair.say; # OUTPUT: a => value B
+$pair.say;  # OUTPUT: «a => value B␤»
 =end code
 
 Please also note that this behavior is totally unrelated to the way used to
@@ -93,9 +93,16 @@ my $v = 'value B';
 my $pair = a => $v;
 $pair.freeze;
 $v = 'value C';
-$pair.say; # OUTPUT: a => value B
+$pair.say; # OUTPUT: «a => value B␤»
 =end code
 
+As Pair implements L<Associative|/type/Associative> role, its value can be
+accessed using Associative subscription operation. Subscrip adverbs work as well.
+
+=for code
+my $pair = a => 5;
+say $pair<a>;        # OUTPUT: «5␤»
+say $pair<a>:exists; # OUTPUT: «True␤»
 
 =head1 Methods