Update independent-routines.pod6

Closes #3730
Closes rakudo/rakudo#4061

Author: Altai-man

doc/Type/independent-routines.pod6

@@ -36,8 +36,13 @@ This can be overridden in any of several ways:
     use MONKEY;             # shortcut that turns on all MONKEY pragmas
     use Test;
 
+    my $init = 0;
+    my $diff = 10;
+    my Str $changer = '$init += ' ~ $diff; # contains a Str object with value '$init += 10'
     # any of the above allows:
-    EVAL "say { 5 + 5 }";   # OUTPUT: «10␤»
+    EVAL $changer;
+    EVAL $changer;
+    say $init;                         # OUTPUT: «20␤»
 
 In case the C<MONKEY-SEE-NO-EVAL> pragma is not activated, the compiler will
 complain with a C<EVAL is a very dangerous function!!!> exception. And it is