Added my relicense doc

Just following the instructions in the email to add my agreement.

RELICENSE/drbobbeaty.md

+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Robert Beaty
+that grants permission to relicense its copyrights in the libzmq C++
+library (ZeroMQ) under the Mozilla Public License v2 (MPLv2) or any other 
+Open Source Initiative approved license chosen by the current ZeroMQ 
+BDFL (Benevolent Dictator for Life).
+
+A portion of the commits made by the Github handle "drbobbeaty", with
+commit author "Bob Beaty <drbob@themanfromspud.com>", are copyright of Robert Beaty .
+This document hereby grants the libzmq project team to relicense libzmq, 
+including all past, present and future contributions of the author listed above.
+
+Robert Beaty
+2019/08/10