feat: add COPYRIGHT file

COPYRIGHT

@@ -0,0 +1,37 @@
+Intellectual Property Notice
+------------------------------
+
+libROM is licensed under the Apache License, Version 2.0 (LICENSE-APACHE
+or http://www.apache.org/licenses/LICENSE-2.0) or the MIT license,
+(LICENSE-MIT or http://opensource.org/licenses/MIT), at your option.
+
+Copyrights and patents in the libROM project are retained by contributors.
+No copyright assignment is required to contribute to libROM.
+
+libROM was originally distributed under a BSD-3 license.
+
+
+SPDX usage
+------------
+
+Individual files contain SPDX tags instead of the full license text.
+This enables machine processing of license information based on the SPDX
+License Identifiers that are available here: https://spdx.org/licenses/
+
+Files that are dual-licensed as Apache-2.0 OR MIT contain the following
+text in the license header:
+
+    SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+
+External Packages
+-------------------
+
+libROM does not currently bundle any external dependencies. However,
+the presentation and naming of licensing and copyright files is
+derived from Spack, which this package's authors gratefully
+acknowledge.
+
+PackageName: Spack
+PackageHomePage: https://github.com/spack/spack
+PackageLicenseDeclared: (Apache-2.0 OR MIT)