Add relicense statement from sradomski

As indicated by author's comment on Github:

#810 (comment)

Author: bluca

RELICENSE/sradomski.md

@@ -0,0 +1,15 @@
+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Stefan Radomski
+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 "sradomski", with
+commit author "Stefan Radomski <[email protected]>", are copyright of Stefan Radomski .
+This document hereby grants the libzmq project team to relicense libzmq,
+including all past, present and future contributions of the author listed above.
+
+Stefan Radomski
+2020/12/20