hdkey copyright

Author: paulmillr

README.md

@@ -249,6 +249,7 @@ It has almost the exact same API than the version `1.x` of
 [`hdkey` from cryptocoinjs](https://github.com/cryptocoinjs/hdkey),
 but it's backed by this package's primitives, and has built-in TypeScript types.
 Its only difference is that it has to be be used with a named import.
+The implementation is [loosely based on hdkey, which has MIT License](#LICENSE).
 
 ```js
 const { HDKey } = require("ethereum-cryptography/hdkey");
@@ -477,6 +478,29 @@ Copyright (c) 2021 Patricio Palladino, Paul Miller, ethereum-cryptography contri
 
 See [LICENSE](./LICENSE) file.
 
+`hdkey` is loosely based on [hdkey](https://github.com/cryptocoinjs/hdkey),
+which has [MIT License](https://github.com/cryptocoinjs/hdkey/blob/3f3c0b5cedb98f971835b5116ebea05b3c09422a/LICENSE)
+
+Copyright (c) 2018 cryptocoinjs
+
+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.
+
 [1]: https://img.shields.io/npm/v/ethereum-cryptography.svg
 [2]: https://www.npmjs.com/package/ethereum-cryptography
 [3]: https://img.shields.io/travis/ethereum/js-ethereum-cryptography/master.svg?label=Travis%20CI