Update README.md

README.md

 RoboCup 2D Half Field Offense
 ===============
 
-[![Build Status](https://travis-ci.org/LARG/HFO.svg?branch=master)](https://travis-ci.org/LARG/HFO)
+[![Build Status](https://travis-ci.org/LARG/HFO.svg?branch=master)](https://travis-ci.org/LARG/HFO) [![No Maintenance Intended](http://unmaintained.tech/badge.svg)](http://unmaintained.tech/)
+
+__WARNING: HFO is not actively maintained!__ We accept pull requests and bug fixes, but please be prepared to do your own debugging in case of a problem. If you'd like to become a maintainer of HFO, get in touch.
 
 ![3 on 3 HFO](https://github.com/mhauskn/HFO/blob/master/img/hfo3on3.png)
 
@@ -81,4 +83,4 @@ for episode in range(5): # replace with xrange(5) for Python 2.X
 ```
 
 ## Documentation
-The state and action spaces provided by the HFO domain are documented in the [manual](doc/manual.pdf).
+The state and action spaces provided by the HFO domain are documented in the [manual](doc/manual.pdf).
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