Add readme and license

frontend/src/lib/LICENSE

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+Copyright (c) 2022 HangarMC and contributors
+
+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.

frontend/src/lib/README.md

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+# HangarLib
+
+This is a shared library used by [Hangar](https://github.com/HangarMC/Hangar)
+and [HangarAuth](https://github.com/HangarMC/HangarAuth).
+
+## Contributing
+
+If you want to edit something in this repository for use in Hangar/HangarAuth, it is usually easier to commit changes in
+the submodule where this is included and to then push the changes to a remote fork. To do that, cd into the submodule's
+directory, switch to or create a branch (`git switch master`), add your GitHub fork as a
+remote (`git remote add fork <fork url>`) and push your code changes to it.
+
+## License
+This project is licensed under the permissive [MIT License](LICENSE).