Update README.md with deprecation note

Author: philipstanislaus

README.md

@@ -1,5 +1,6 @@
-# Performant array to tree
+# ⛔️ DEPRECATED Performant array to tree
 
+[![No Maintenance Intended](http://unmaintained.tech/badge.svg)](http://unmaintained.tech/)
 [![npm version](https://img.shields.io/npm/v/performant-array-to-tree.svg)](https://www.npmjs.com/package/performant-array-to-tree)
 [![minified size](https://img.shields.io/badge/minified_size-2.1_kb-brightgreen.svg)](https://github.com/philipstanislaus/performant-array-to-tree/blob/main/build/arrayToTree.min.js)
 [![CircleCI](https://circleci.com/gh/philipstanislaus/performant-array-to-tree/tree/main.svg?style=shield&circle-token=01828caf71908b915230609847a12272cc80c54d)](https://circleci.com/gh/philipstanislaus/performant-array-to-tree/tree/main)
@@ -8,6 +9,9 @@
 [![typings included](https://img.shields.io/badge/typings-included-brightgreen.svg)](#typescript)
 [![npm license](https://img.shields.io/npm/l/performant-array-to-tree.svg)](https://www.npmjs.com/package/performant-array-to-tree)
 
+> [!CAUTION]
+> This repository is no longer maintained. Consider the section below for alternatives.
+
 Converts an array of items with ids and parent ids to a nested tree in a performant way (time complexity `O(n)`). Runs in browsers and node.
 
 ## Why another package