Add QR code troubleshooting to user guide.

Closes #49.

react-native-scripts/template/README.md

@@ -23,6 +23,7 @@ Below you'll find information about performing common tasks. The most recent ver
 * [Troubleshooting](#troubleshooting)
   * [Networking](#networking)
   * [iOS Simulator won't open](#ios-simulator-wont-open)
+  * [QR Code does not scan](#qr-code-does-not-scan)
 
 ## Updating to New Releases
 
@@ -152,3 +153,9 @@ There are a few steps you may want to take to troubleshoot these kinds of errors
 1. Make sure Xcode is installed and open it to accept the license agreement if it prompts you. You can install it from the Mac App Store.
 2. Open Xcode's Preferences, the Locations tab, and make sure that the `Command Line Tools` menu option is set to something. Sometimes when the CLI tools are first installed by Homebrew this option is left blank, which can prevent Apple utilities from finding the simulator. Make sure to re-run `npm/yarn run ios` after doing so.
 3. If that doesn't work, open the Simulator, and under the app menu select `Reset Contents and Settings...`. After that has finished, quit the Simulator, and re-run `npm/yarn run ios`.
+
+### QR Code does not scan
+
+If you're not able to scan the QR code, make sure your phone's camera is focusing correctly, and also make sure that the contrast on the two colors in your terminal is high enough. For example, WebStorm's default themes may [not have enough contrast](https://github.com/react-community/create-react-native-app/issues/49) for terminal QR codes to be scannable with the system barcode scanners that the Expo app uses.
+
+If this causes problems for you, you may want to try changing your terminal's color theme to have more contrast, or running Create React Native App from a different terminal. You can also manually enter the URL printed by the packager script in the Expo app's search bar to load it manually.