add sunset message

README.md

@@ -1,4 +1,5 @@
-# Autocomplete+ package
+##### Atom and all repositories under Atom will be archived on December 15, 2022. Learn more in our [official announcement](https://github.blog/2022-06-08-sunsetting-atom/)
+ # Autocomplete+ package
 [![macOS Build Status](https://travis-ci.org/atom/autocomplete-plus.svg?branch=master)](https://travis-ci.org/atom/autocomplete-plus) [![Windows Build status](https://ci.appveyor.com/api/projects/status/9bpokrud2apgqsq0/branch/master?svg=true)](https://ci.appveyor.com/project/Atom/autocomplete-plus/branch/master) [![Dependency Status](https://david-dm.org/atom/autocomplete-plus.svg)](https://david-dm.org/atom/autocomplete-plus)
 
 Displays possible autocomplete suggestions on keystroke (or manually by typing `ctrl-space`) and inserts a suggestion in the editor if confirmed.