Add a note for OSX users about watchman and jest

Minor additional information on how to solve watchman problems reported in facebook#713 and facebook#1767

Author: dmr

packages/react-scripts/template/README.md

@@ -675,6 +675,14 @@ The watcher includes an interactive command-line interface with the ability to r
 
 ![Jest watch mode](http://facebook.github.io/jest/img/blog/15-watch.gif)
 
+>**A note for Mac OSX users**
+
+>If you start `npm test` and the execution hangs there might be a problem with your watchman installation as discovered in #713 and #1767.
+
+> To solve the issues first make sure you run the latest verision: `brew install watchman` (4.7.0).
+Then execute `launchctl unload -F ~/Library/LaunchAgents/com.github.facebook.watchman.plist`. After these steps the issues should be resolved.
+
+
 ### Version Control Integration
 
 By default, when you run `npm test`, Jest will only run the tests related to files changed since the last commit. This is an optimization designed to make your tests runs fast regardless of how many tests you have. However it assumes that you don’t often commit the code that doesn’t pass the tests.