Update Functions CI article to mention the Project app setting

[lindydonna]

I've seen a few questions from customers about how to set the right directory for deployment.

I suggest we updated this article: https://docs.microsoft.com/en-us/azure/azure-functions/functions-continuous-deployment with the following:

• Link to https://github.com/projectkudu/kudu/wiki/Customizing-deployments
• Show a sample .deployment file such as the following:
  [config] project = MyFunctionRoot

[SyntaxC4]

I have documented some of this as part of the ARM Template document: https://docs.microsoft.com/en-us/azure/azure-functions/functions-infrastructure-as-code