Note about reinstalling fbprophet after upgrading pystan

README.md

@@ -48,6 +48,8 @@ The major dependency that Prophet has is `pystan`.   PyStan has its own [install
 
 After installation, you can [get started!](https://facebook.github.io/prophet/docs/quick_start.html#python-api)
 
+If you upgrade the version of PyStan installed on your system, you may need to reinstall fbprophet ([see here](https://github.com/facebook/prophet/issues/324)).
+
 ### Windows
 
 On Windows, PyStan requires a compiler so you'll need to [follow the instructions](http://pystan.readthedocs.io/en/latest/windows.html).  The key step is installing a recent [C++ compiler](http://landinghub.visualstudio.com/visual-cpp-build-tools).