docs: prepare project for archival

Add a message to the readme explaining my motivation for putting this project on hold.

Author: pwbriggs

README.md

@@ -6,6 +6,12 @@
 [![Time of last commit](https://img.shields.io/github/last-commit/pwbriggs/library?logo=github)](https://github.com/pwbriggs/library/commits/)
 [![Status of CI tests on GitHub](https://img.shields.io/github/actions/workflow/status/pwbriggs/library/ci.yml?label=CI+tests&logo=github)](https://github.com/pwbriggs/library/actions)
 
+> [!WARNING]
+>
+> This project is no longer maintained as of June 2025. The ecosystem is moving delightfully fast, with Remix and React Router at last coming together, and Vite taking huge strides. This is *awesome* and I can't wait to use all this amazing new tooling, but at this point this project has such a lack of features that the maintenence load to keep up with the ecosystem is not worth it.
+>
+> I still think this would be a cool project to make, but I do not have the time or dedication for it at present.
+
 Open-source software for cataloging and loaning items in a library.
 
 If you have feature requests or suggestions, don't hesitate to open an issue!