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 run 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 (like an API endpoint). Project Acorn 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
+
+To deploy an azure function application using Project Acorn:
+
+![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 would take you to Azure portal
+  to create a subscription.
+
+- Enter a name for your function app. This name has to be globally unique since your app will be available as
+  `<function_app_name>.azurewebsites.net` after.
+
+- 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 basically what programming language/framework you want to write your
+  functions in.
+
+- Select number of functions you think you might need for your applications. Think about this as number of endpoints you
+  think 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 variable
+name. For ex: `<function_app_name>.azurewebsites.net\api\<function_name>?name=John+Doe` will return _Hello, John Doe_.
+
+## How this works
+
+Once you hit generate, Project acorn creates a directory with the same name as your _function 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 _arm-templates_ directory (under your generated project).
+
+## Functions app in Azure Portal
+
+![azure-functions-portal](../resources/azure-functions-portal.png)
+
+You can configure your functions application for advanced settings (like configuring domain, storage accounts etc.),
+delete your application etc. from your [azure portal](https://portal.azure.com). Once you login to the portal, select
+functions app from the menu bar on left side and select your application. Your individual functions are listed under
+_functions_ and you can monitor them/integrate them here. Pretty much anything you need to manage about your 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 right away instead of manually deploying the new changes.
+Once you have installed this application, here's what you need to do to deploy your changes:
+
+![azure-functions-extension](../resources/azure-functions-extension.png)
+
+- Open your functions application directory in a new VSCode window. Edit your function/functions file.
+
+- Select Azure from the activity bar on VSCode and under 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, delete all references to it and deploy again.
+
+### Deploying manually
+
+If you don't want to install the extension (it is _recommended_ that you install it to make your workflow easier), follow
+one of the ways mentioned 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!