Fixed a documentation error in protocol.txt

Prior to the documentation told users to pass 0 in as
the first argument to write messages, when they should
be outting in their local-id. It is now corrected.

Change-Id: Ia2c6c84f95383baa5ca471493a29a39e5173b604
Signed-off-by: Derrick Bonafilia <dbonafilia@google.com>