Indicate differences between this repo and original repo

I uploaded this code as a new repo rather than forking from original one 
because if the original author deletes his repo, it will also mess with 
the forked repo. Removing the forked status prevents this from 
occurring.

README.md

@@ -4,6 +4,8 @@
 
 Multi-way trees (Rose Trees) with Zippers.
 
+This is a maintained fork of `purescript-tree`.
+
 ## Installation
 
 ```