Simplify requirements and update readme

Author: kraigb

README.md

@@ -1,6 +1,7 @@
 # Python/Flask Tutorial for Visual Studio Code
 
 * This sample contains the completed program from the tutorial, make sure to visit the link: [Using Flask in Visual Studio Code](https://code.visualstudio.com/docs/python/tutorial-flask). Intermediate steps are not included.
+* To run the app, first run use `set FLASK_APP=hello_app:app` (Windows cmd) or `FLASK_APP=hello_app:app` (macOS/Linux).
 * It also contains the Dockerfile and uwsgi.ini files necessary to build a container with a production server. The resulting image works both locally and when deployed to Azure App Service. See [Deploy Python using Docker containers](https://code.visualstudio.com/docs/python/tutorial-deploy-containers).
 
 ## Navigation

requirements.txt

@@ -1,6 +1 @@
-click==6.7
-Flask==1.0.2
-itsdangerous==0.24
-Jinja2>=2.10.1
-MarkupSafe==1.0
-Werkzeug==0.15.5
+Flask