pw_hdlc: fix python example for encode

No testing done.

Change-Id: Ifdcf117415ca8ced627b934cb683286c26252f9c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/45300
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Paul Mathieu <paulmathieu@google.com>
diff --git a/pw_hdlc/docs.rst b/pw_hdlc/docs.rst
index 6791855..e323224 100644
--- a/pw_hdlc/docs.rst
+++ b/pw_hdlc/docs.rst
@@ -134,7 +134,8 @@
   from pw_hdlc import encode
 
   ser = serial.Serial()
-  ser.write(encode.ui_frame(b'your data here!'))
+  address = 123
+  ser.write(encode.ui_frame(address, b'your data here!'))
 
 Decoder
 -------