Add main.py

Following basic Flask on Google App Engine tutorial:

https://realpython.com/python-web-applications/#build-a-basic-python-web-application

main.py

@@ -0,0 +1,13 @@
+from flask import Flask
+
+
+app = Flask(__name__)
+
+
+@app.route("/")
+def index():
+
+    return "Congratulations, it's a web app!"
+
+if __name__ == "__main__":
+    app.run(host="127.0.0.1", port=8080, debug=True)