Update gettingstarted.md (#11094)

* Update gettingstarted.md

1. Flask app was running in the wrong port.
2. 5000 port was not exposed in Dockerfile

* Update gettingstarted.md

mistook Redis port to flask port.

compose/gettingstarted.md

@@ -90,6 +90,7 @@ following:
     COPY requirements.txt requirements.txt
     RUN pip install -r requirements.txt
     COPY . .
+    EXPOSE 5000
     CMD ["flask", "run"]
 
 This tells Docker to: