Adds string contextualizer ~ refs #1225

Author: JJ

doc/Language/contexts.pod6

@@ -59,6 +59,13 @@ Or when smart-matching to a regular expression:
 
 In general, the L<C<Str> routine|/routine/Str> will be called on a variable to contextualize it; since this method is inherited from L<Mu>, it is always present, but it is not always guaranteed to work. In some core classes it will issue a warning.
 
+L<C<~>|/routine/~> is the (unary) string contextualizer. As an operator, it concatenates strings, but as a prefix operator it becomes the string context operator.
+
+=begin code
+my @array = [ [1,2,3], [4,5,6]];
+say ~@array; # OUTPUT: «1 2 3 4 5 6␤»
+=end code
+
 =end pod
 
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