Improve ff() examples

- Add an element to the beginning and end of the arrays
  used in the ff() (and related) examples. This is to also
  show the main feature of ff() when the read looks for
  specific usage examples.

Author: Salve J. Nilsen

doc/Language/operators.rakudoc

@@ -2859,7 +2859,7 @@ condition).
 
 A comparison:
 
-    my @list = <A B C>;
+    my @list = <X A B C Y>;
     say $_ if /A/ ff /C/ for @list;    # OUTPUT: «A␤B␤C␤»
     say $_ if /A/ ^ff /C/ for @list;   # OUTPUT: «B␤C␤»
 
@@ -2874,7 +2874,7 @@ This operator cannot be overloaded, as it's handled specially by the compiler.
 Works like L<ff|/routine/ff>, except it does not return C<True> for items matching the
 stop condition (including items that first matched the start condition).
 
-    my @list = <A B C>;
+    my @list = <X A B C Y>;
     say $_ if /A/ ff /C/ for @list;    # OUTPUT: «A␤B␤C␤»
     say $_ if /A/ ff^ /C/ for @list;   # OUTPUT: «A␤B␤»
 
@@ -2889,7 +2889,7 @@ This operator cannot be overloaded, as it's handled specially by the compiler.
 Works like L<ff|/routine/ff>, except it does not return C<True> for items matching either
 the stop or start condition (or both).
 
-    my @list = <A B C>;
+    my @list = <X A B C Y>;
     say $_ if /A/ ff /C/ for @list;    # OUTPUT: «A␤B␤C␤»
     say $_ if /A/ ^ff^ /C/ for @list;  # OUTPUT: «B␤»
 
@@ -2925,7 +2925,7 @@ This operator cannot be overloaded, as it's handled specially by the compiler.
 
 Like L<fff|/routine/fff>, except it does not return true for matches to the left argument.
 
-    my @list = <A B C>;
+    my @list = <X A B C Y>;
     say $_ if /A/ fff /C/ for @list;   # OUTPUT: «A␤B␤C␤»
     say $_ if /A/ ^fff /C/ for @list;  # OUTPUT: «B␤C␤»
 
@@ -2940,7 +2940,7 @@ This operator cannot be overloaded, as it's handled specially by the compiler.
 Like L<fff|/routine/fff>, except it does not return true for matches to the right
 argument.
 
-    my @list = <A B C>;
+    my @list = <X A B C Y>;
     say $_ if /A/ fff /C/ for @list;   # OUTPUT: «A␤B␤C␤»
     say $_ if /A/ fff^ /C/ for @list;  # OUTPUT: «A␤B␤»
 
@@ -2955,7 +2955,7 @@ This operator cannot be overloaded, as it's handled specially by the compiler.
 Like L<fff|/routine/fff>, except it does not return true for matches to either the left or
 right argument.
 
-    my @list = <A B C>;
+    my @list = <X A B C Y>;
     say $_ if /A/ fff /C/ for @list;   # OUTPUT: «A␤B␤C␤»
     say $_ if /A/ ^fff^ /C/ for @list; # OUTPUT: «B␤»