decklink: Add license declaration files

plugins/decklink/LICENSE.decklink-sdk

@@ -0,0 +1,30 @@
+decklink-sdk is licensed under the Boost Software License 1.0 (BSL-1.0).
+
+The license text is reproduced in full below:
+
+/* -LICENSE-START-
+** Copyright (c) 2020 Blackmagic Design
+**
+** Permission is hereby granted, free of charge, to any person or organization
+** obtaining a copy of the software and accompanying documentation covered by
+** this license (the "Software") to use, reproduce, display, distribute,
+** execute, and transmit the Software, and to prepare derivative works of the
+** Software, and to permit third-parties to whom the Software is furnished to
+** do so, all subject to the following:
+**
+** The copyright notices in the Software and this entire statement, including
+** the above license grant, this restriction and the following disclaimer,
+** must be included in all copies of the Software, in whole or in part, and
+** all derivative works of the Software, unless such copies or derivative
+** works are solely in the form of machine-executable object code generated by
+** a source language processor.
+**
+** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+** IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+** FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+** SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+** FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+** ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+** DEALINGS IN THE SOFTWARE.
+** -LICENSE-END-
+*/