RELICENSE: Start collecting MPLv2 license grants

RELICENSE/README.md

+# Permission to Relicense under MPLV2
+
+This directory collects grants from individuals and firms that hold
+copyrights in ZeroMQ to permit licensing the ZeroMQ code under
+the [Mozilla Public License, version
+2](https://www.mozilla.org/en-US/MPL/2.0/).  See [GitHub Pull
+Request #1917](https://github.com/zeromq/libzmq/pull/1917) and
+[original iMatix zeromq-dev license
+grant](http://lists.zeromq.org/pipermail/zeromq-dev/2016-April/030288.html)
+for some background information.
+
+Please create a separate file in this directory for each individual
+or firm holding copyright in ZeroMQ, named after the individual or
+firm holding the copyright.
+
+Each patch must be made with a GitHub handle that is clearly
+associated with the copyright owner, to guarantee the identity of
+the signatory.  Please avoid changing the files created by other
+individuals or firms granting a copyright license over their
+copyrights (if rewording is required contact them and ask them to
+submit an updated version).  This makes it easier to verify that
+the license grant was made by an authorized GitHub account.