Added instrutions to add platform-tools to Path. (#713)

* Added instrutions to add platform-tools to Path.

This allows windows to find adb.exe, a file required for react-native run-android to work properly.

* removed wrong block class

docs/getting-started.md

@@ -405,6 +405,16 @@ You can find the actual location of the SDK in the Android Studio "Preferences"
 
 Open a new Command Prompt window to ensure the new environment variable is loaded before proceeding to the next step.
 
+#### 4. Add platform-tools to Path
+
+Open the System pane under **System and Security** in the Windows Control Panel, then click on **Change settings...**. Open the **Advanced** tab and click on **Environment Variables...**. Select the **Path** variable, then click **Edit**. Click **New** and add the path to platform-tools to the list.
+
+The default location for this folder is:
+
+```powershell
+c:\Users\YOUR_USERNAME\AppData\Local\Android\Sdk\platform-tools
+```
+
 <block class="native linux android" />
 
 ### Watchman