IVGCVSW-7024 Add missing license info for reuse lint

Signed-off-by: Jim Flynn <jim.flynn@arm.com>
Change-Id: I97dee6982e0a7be01c13e9e803c0997547a39ff1
diff --git a/third-party/cxxopts/README.md.license b/third-party/cxxopts/README.md.license
new file mode 100644
index 0000000..bf1b5b5
--- /dev/null
+++ b/third-party/cxxopts/README.md.license
@@ -0,0 +1,4 @@
+#
+# Copyright (c) 2014 Jarryd Beck
+# SPDX-License-Identifier: MIT
+#