Add deprecation notice (#3874)

Task/Issue URL: https://app.asana.com/0/72649045549333/1209418366154030
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Description:

This PR adds a deprecation notice to the README.

Author: samsymons

README.md

@@ -1,9 +1,10 @@
 # DuckDuckGo for macOS
 
-We are excited to engage the community in development!
+> [!IMPORTANT]  
+> 👋 Thanks for your interest in DuckDuckGo! The source code for this project has been moved to [duckduckgo/apple-browsers](https://github.com/duckduckgo/apple-browsers) and this repo no longer accepts contributions.
+> Please file any bug reports or feature requests in the new repo.
 
-## We are hiring!
-DuckDuckGo is growing fast and we continue to expand our fully distributed team. We embrace diverse perspectives, and seek out passionate, self-motivated people, committed to our shared vision of raising the standard of trust online. If you are a senior software engineer, visit our [careers](https://duckduckgo.com/hiring/#open) page to find out more about our openings!
+We are excited to engage the community in development!
 
 ## Building