You can use the Third Party Notices.md and LICENSE.md files to make sure your package meets any legal requirements. For example, here is a sample license file from the Unity Timeline package:
Unity Timeline copyright © 2017-2019 Unity Technologies ApS
Licensed under the Unity Companion License for Unity-dependent projects--see [Unity Companion License](http://www.unity3d.com/legal/licenses/Unity_Companion_License).
Unless expressly provided otherwise, the Software under this license is made available strictly on an “AS IS” BASIS WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. Please review the license for details on these and other terms and conditions.
If your package has third-party elements, you can include the licenses in a Third Party Notices.md file. You can include a Component Name, License Type, and Provide License Details section for each license you want to include. For example:
This package contains third-party software components governed by the license(s) indicated below:
Component Name: Semver
License Type: "MIT"
[SemVer License](https://github.com/myusername/semver/blob/master/License.txt)
Component Name: MyComponent
License Type: "MyLicense"
[MyComponent License](https://www.mycompany.com/licenses/License.txt)
Note: The URL in the Provide License Details section should point to a location that contains the reproduced license and the copyright information (if applicable).