Added a new troubleshoot (reduxjs#691)

Accessing PropTypes via the main React package is deprecated. Use the prop-types package from npm instead.

Author: DanZeuss

docs/troubleshooting.md

@@ -2,6 +2,11 @@
 
 Make sure to check out [Troubleshooting Redux](http://redux.js.org/docs/Troubleshooting.html) first.
 
+### I'm getting the following alert: Accessing PropTypes via the main React package is deprecated. Use the prop-types package from npm instead.
+This warning is shown when using react 15.5.*. basically, now it's just a warning, but in react16 the application might break. the PropTypes should now be imported from 'prop-types' package, and not from the react package.
+
+Update to the latest version of react-redux.
+
 ### My views aren’t updating!
 
 See the link above.