readme: coinrun version differences

README.md

@@ -8,7 +8,7 @@
 
 <img src="https://raw.githubusercontent.com/openai/procgen/master/screenshots/procgen.gif">
 
-These environments are associated with the paper [Leveraging Procedural Generation to Benchmark Reinforcement Learning](https://cdn.openai.com/procgen.pdf) [(citation)](#citation).  The code for running some experiments from the paper is in the [train-procgen](https://github.com/openai/train-procgen) repo.
+These environments are associated with the paper [Leveraging Procedural Generation to Benchmark Reinforcement Learning](https://cdn.openai.com/procgen.pdf) [(citation)](#citation).  The code for running some experiments from the paper is in the [train-procgen](https://github.com/openai/train-procgen) repo.  For those familiar with the original [CoinRun environment](https://github.com/openai/coinrun), be sure to read the updated CoinRun description below as there have been subtle changes to the environment.
 
 Compared to [Gym Retro](https://github.com/openai/retro), these environments are: