added functions doc

docs/services/azure-functions.md

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+# Azure Functions
+
+Azure Functions is a serverless compute service that enables you to run code on-demand without having to explicitly
+provision or manage infrastructure. Think of it as deploying functions that executes on pre-defined triggers instead of
+having to write and manage a full-fledged server yourself. One of the most commonly used triggers is an HTTPTrigger which
+is a function that runs whenever it receives an HTTP request. This is essentially the same as an API endpoint. Web
+Template Studio allows you to deploy a function app with multiple 'hello world' HTTPTrigger functions (maximum of 10) so
+you can get to writing your business logic as soon as possible!
+
+## Getting started
+
+Deploying an Azure Function application using Web Template Studio:
+
+![azure-functions-modal](../resources/azure-functions-modal.png)
+
+- Click _Add Resource_ on Azure Functions under _Services_ tab
+
+- Select a _Subscription_ and _Resource Group_ from the _Create Functions Application_ tab that just opened. Use _Create
+  New_ if you want to create a new subscription or resource group. _**Note:**_ New subscription will take you to the Azure
+  portal to create a subscription.
+
+- Enter an _App Name_ for your function app. This name has to be globally unique since your app will be available as
+  `<function_app_name>.azurewebsites.net`.
+
+- Select a _Location_ where your function app will be deployed. You want it to be closer to your users (or servers if it's
+  running as a back-end service helper).
+
+- Select a _Runtime_ for your functions. This is the programming language/framework you want to write your
+  functions in.
+
+- Select the _Number of Functions_ needed for your application. This number can be thought of as the number of endpoints
+  your application would need. You can rename your functions from the summary bar on the right side of the
+  application. These would be available as `<function_app_name>.azurewebsites.net\api\<function_name>`.
+
+The _hello world_ functions deployed are pretty basic and just return _"Hello, `<name>`"_ on a query/header with the
+variable 'name'. For example: `<function_app_name>.azurewebsites.net\api\<function_name>?name=John+Doe` will return
+_"Hello, John Doe"_.
+
+## How this works
+
+Once you hit generate, Web Template Studio creates a directory with the same name as your Function's _App Name_ under your
+generated project. This is compressed to a _.zip_ and deployed (using kudu zip deploy) to your newly created function
+application. _**Note:**_ For advanced users, the _arm templates_ used to deploy your application are also available
+under the _arm-templates_ directory (inside your generated project).
+
+## Functions app in Azure Portal
+
+![azure-functions-portal](../resources/azure-functions-portal.png)
+
+You can configure your Function Application's advanced settings (like configuring a domain, storage accounts,
+delete your application etc.) from the [azure portal](https://portal.azure.com). Once you login to the portal, select
+**Function Apps** from the menu bar on the left side and select your application. Your individual functions are listed
+under _Functions_ and you can monitor/integrate them here. Everything you need to manage/configure about your Function
+Application can be done through the portal.
+
+## Editing your functions and deploying the changes
+
+We strongly encourage you to install the [Azure Functions](https://marketplace.visualstudio.com/items?
+itemName=ms-azuretools.vscode-azurefunctions) extension for VSCode by **Microsoft** to manage your application. This
+enables you to deploy your changes with a single click and test them out immediately instead of manually deploying the
+new changes. Once you have installed this extension, here's what you need to do to deploy your changes:
+
+![azure-functions-extension](../resources/azure-functions-extension.png)
+
+- Open your Function Application's directory in a new VSCode window. Edit your function file(s).
+
+- Select Azure from the activity bar on VSCode and in the _Functions_ tab bar, click the `Deploy to function app...`
+  button and select your function application from the menu.
+
+- You can also add new functions using the `Create function...` button.
+
+- To remove a function, simply delete the corresponding files and all references to it and deploy again.
+
+### Deploying manually
+
+If you do not want to install the extension (it is _recommended_ that you install it to make your workflow easier), follow
+one of the methods in the [Azure app service zip deploy tutorial](https://docs.microsoft.com/en-us/azure/app-service/
+deploy-zip) to manually deploy your updated functions!