Add deprecation notice

Author: garyb

.eslintrc.json

@@ -1,16 +1,5 @@
-# purescript-maps
+# DEPRECATED
 
-[![Latest release](http://img.shields.io/github/release/purescript/purescript-maps.svg)](https://github.com/purescript/purescript-maps/releases)
-[![Build status](https://travis-ci.org/purescript/purescript-maps.svg?branch=master)](https://travis-ci.org/purescript/purescript-maps)
+The library is no longer maintained under this repository, it has been merged into to [`purescript-ordered-collections`](https://github.com/purescript/purescript-ordered-collections).
 
-Purely-functional map data structures.
-
-## Installation
-
-```
-bower install purescript-maps
-```
-
-## Documentation
-
-Module documentation is [published on Pursuit](http://pursuit.purescript.org/packages/purescript-maps).
+[The previous releases](https://github.com/purescript-deprecated/purescript-maps/releases) will continue to work for older libraries that still depend on them.