docs: add third party notices for vendored companion

THIRD_PARTY_NOTICES.md

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+# Third Party Notices
+
+This project distributes third party software. The components below are
+included under their respective licenses.
+
+## idb-companion
+
+- Project: idb (https://github.com/facebook/idb)
+- Version: 1.1.8
+- Copyright: Copyright (c) Meta Platforms, Inc. and affiliates.
+- License: MIT
+
+The simulator companion is vendored as a prebuilt binary artifact (the
+`idb_companion` executable together with its runtime frameworks). It is
+embedded into the sanderling binary at build time and extracted to a local
+directory at runtime.
+
+### MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.