Updating sample for app deploy addpy to include instructions on how to call the REST api.

Author: jeroenterheerdt

samples/features/sql-big-data-cluster/app-deploy/addpy/README.md

@@ -73,7 +73,58 @@ To run this sample, you need the following prerequisites.
       "success": true
     }
     ```
-6. You can clean up the sample by running the following commands:
+6. Any app you create is also accessible using a RESTful web service that is [Swagger](swagger.io) compliant. You can get the endpoint for the web service by running:
+   ```bash
+   mssqlctl app describe --name addpy --version [version]
+   ```
+   This will return an output much like the following:
+   ```json
+   {
+      "input_param_defs": [
+        {
+          "name": "x",
+          "type": "int"
+        },
+        {
+          "name": "y",
+          "type": "int"
+        }
+      ],
+      "links": {
+        "app": "https://[IP]:[PORT]/api/app/addpy/[version]",
+        "swagger": "https://[IP]:[PORT]/api/app/addpy/[version]/swagger.json"
+      },
+      "name": "addpy",
+      "output_param_defs": [
+        {
+          "name": "result",
+          "type": "int"
+        }
+      ],
+      "state": "Ready",
+      "version": "[version]"
+    }
+   ```
+   Note the IP address and the port number in this output. Open the following URL in your browser:
+   `https://[IP]:[PORT]/api/docs/swagger.json`. You will have to log in with the same credentials you used for `mssqlctl login`. The contents of the `swagger.json` you can paste into [Swagger Editor](https://editor.swagger.io) to understand what methods are available:
+   ![API swagger](api_swagger.png)
+
+   Notice the `app` GET method as well as the `token` POST method. Since the authentication for apps uses JWT tokens you will need to get a token my using your favorite tool to make a POST call to the `token` method. Here is an example of how to do just that in [Postman](https://www.getpostman.com/):
+   ![Postman Token](postman_token.png)
+
+   The result of this request will give you an `access_token`, which you will need to call the URL to run the app.
+   
+   > *Optional*: If you want, you can open the URL for the `swagger` that was returned when you ran `mssqlctl app describe --name addpy --version [version]` in your browser. You will have to log in with the same credentials you used for `mssqlctl login`. The contents of the `swagger.json` you can paste into [Swagger Editor](https://editor.swagger.io). You will see that the web service exposes the `run` method.
+
+   You can use your favorite tool to call the `run` method (`https://[IP]:[PORT]/api/app/addpy/[version]/run`), passing in the parameters in the body of your POST request as json. In this example we will use [Postman](https://www.getpostman.com/). Before making the call, you will need to set the `Authorization` to `Bearer Token` and paste in the token you retrieved earlier. This will set a header on your request. See the screenshot below.
+   ![Postman Run Headers](postman_run_1.png)
+   Next, in the requests body, pass in the parameters to the app you are calling and set the `content-type` to `application/json`:
+   ![Postman Run Body](postman_run_2.png)
+   When you send the request, you will get the same output as you did when you ran the app through `mssqlctl app run`:
+   ![Postman Run Result](postman_result.png)
+   You have now successfully called the app through the web service!
+   
+7. You can clean up the sample by running the following commands:
     ```bash
     # delete app
     mssqlctl app delete --name addpy --version [version]