Add Troubleshooting Guide to Sidebar.

Summary:
Doing this will make it easier for us to migrate docs to the new site.
Closes https://github.com/facebook/react-native/pull/15658

Differential Revision: D5710584

Pulled By: hramos

fbshipit-source-id: 021ed1cd71b77de05deebdc8045e5e409071c95f

docs/Troubleshooting.md

@@ -2,10 +2,13 @@
 id: troubleshooting
 title: Troubleshooting
 layout: docs
-category: Quick Start
+category: Guides
 permalink: docs/troubleshooting.html
+next: native-modules-ios
+previous: upgrading
 ---
 
+
 These are some common issues you may run into while setting up React Native. If you encounter something that is not listed here, try [searching for the issue in GitHub](https://github.com/facebook/react-native/issues/).
 
 ### Port already in use

docs/Upgrading.md

@@ -4,7 +4,7 @@ title: Upgrading to new React Native versions
 layout: docs
 category: Guides
 permalink: docs/upgrading.html
-next: native-modules-ios
+next: troubleshooting
 previous: running-on-device
 ---