Improve minmax: example with same values.

Author: fluca1978

doc/Language/operators.pod6

@@ -1853,6 +1853,13 @@ For instance:
 'z' minmax 'k';  # "k".."z"
 =end code
 
+If the lowest and highest values coincide, the operator returns a L<Range>
+made by the same value:
+
+=begin code
+1 minmax 1;  # 1..1
+=end code
+
 =head1 Conditional Operator Precedence
 
 =head2 infix C<?? !!>