Update overall project status in README (#3136)

Summary:
Draft.js has been internally unmaintained at Meta for a while. Instead, we've been building and migrating to our replacement text editing framework, Lexical.

This PR marks Draft.js as unmaintained for external users.

Pull Request resolved: #3136

Reviewed By: tylerjbainbridge, acywatson

Differential Revision: D35609270

Pulled By: thegreatercurve

fbshipit-source-id: 2bbfc60024fbd49afad811c5baa2f005803483fd

README.md

@@ -19,7 +19,13 @@
 </p>
 
 --------------------
+## Status
 
+**THIS PROJECT IS CURRENTLY IN MAINTENANCE MODE. It will not receive any feature updates, only critical security bug patches. On 31st December 2022 the repo will be fully archived.**
+
+For users looking for an open source alternative, Meta have been working on migrating to a new framework, called [Lexical](/~https://github.com/facebook/lexical). It's still experimental, and we're working on adding migration guides, but, we believe, it provides a more performant and accessible alternative.
+
+--------------------
 Draft.js is a JavaScript rich text editor framework, built for React and
 backed by an immutable model.