Revise README for project relocation to Codeberg

Updated README to reflect the project's move to Codeberg and archive status on GitHub.

Author: bitfl0wer

README.md

@@ -3,6 +3,10 @@
 >
 > We have moved to [Codeberg](https://codeberg.org/polyphony) as our primary Git Forge, and the project is *alive and well* over there! :purple_heart: The GitHub repositories will be archived and potentially deleted in the future.
 
+
+<details>
+  <summary>Old README (outdated!)</summary>
+
 [![FAQ-shield]][FAQ]
 
 # Website
@@ -70,3 +74,5 @@ contents hosting service.
 
 [FAQ-shield]: https://img.shields.io/badge/Frequently_Asked_Questions_(FAQ)-ff62bd
 [FAQ]: https://github.com/polyphony-chat/.github/blob/main/FAQ.md
+
+</details>