Document behaviour on .out-buffer changes

and add a code example

Author: zoffixznet

doc/Type/IO/Handle.pod6

@@ -493,6 +493,18 @@ Lastly, can take a C<Nil> to enable TTY-based buffering control: if
 the handle L<is a TTY|/routine/t>, the buffering is disabled, otherwise,
 default, implementation-defined buffer size is used.
 
+See L<flush> to write out data currently in the buffer. Changing buffer
+size flushes the filehandle.
+
+=for code :skip-test
+given 'foo'.IO.open: :w, :1000out-buffer {
+    .say: 'Hello world!'; # buffered
+    .out-buffer = 42;       # buffer resized; previous print flushed
+    .say: 'And goodbye';
+    .close; # closing the handle flushes the buffer
+}
+
+
 =head2 method put
 
 Defined as: