chore: add deprecation note on README.md (#173)

# Description

This PR add a small deprecation note on our README.md before archiving
the repository so users now were to go for future changes.

**Type of change**

(Please delete options that are not relevant. Remember to title the PR
according to the type of change)

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] Refactor (change restructuring the codebase without changing
functionality)
- [ ] Improvement (change adding some improvement to an existing
functionality)
- [x] Documentation update

**How Has This Been Tested**

(Please describe the tests that you ran to verify your changes. And
ideally, reference `tests`)

- [x] Not needed. 

**Checklist**

- [ ] I added relevant documentation
- [ ] follows the style guidelines of this project
- [ ] I did a self-review of my code
- [ ] I made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I filled out [the contributor form](https://tally.so/r/n9XrxK)
(see text above)
- [ ] I have added relevant notes to the CHANGELOG.md file (See
https://keepachangelog.com/)

README.md

@@ -1,3 +1,6 @@
+> [!IMPORTANT]
+> This repository has been archived and is no longer maintained. If you are looking for the latest version of the Argilla server, please visit the [Argilla mono repo](https://github.com/argilla-io/argilla), code for Argilla server is located at [`argilla-server`](https://github.com/argilla-io/argilla/tree/develop/argilla-server) folder.
+
 <h1 align="center">
   <a href=""><img src="https://github.com/dvsrepo/imgs/raw/main/rg.svg" alt="Argilla" width="150"></a>
   <br>