Add COPYRIGHT.md and LICENSE.md

bk: 676e8a01o45iNDFAA7ni40qVxaYHAw

Author: ntpreleng

ChangeLog

@@ -1,6 +1,7 @@
 ---
 * [Bug 3960] Remove duplicate ntp.conf.def content, reported by
              Ulrich Windl. <stenn@ntp.org>
+* Add COPYRIGHT.md and LICENSE.md.  <stenn@ntp.org>
 * Makefile.am: Fix distcheck problem with check-local.  <stenn@ntp.org>
 * Add .github to the top-level tree. <dlavigne@nwtime.org>
 * build script: Use hostname.site for NTF build hosts.  Use the full