added README for flask backend

backends/flask-backend/README.md

+
+
+# Flask Backend
+
+- *Pre-requisite:* Please make sure that DB container is runnning with following information available. 
+    -  DB_HOST
+    -  DB_NAME
+    -  DB_PORT
+    -  DB_USER
+    -  DB_PASSWORD
+
+
+    ( Note: This container is tested with MariaDB container given in DB section, in case of different DB, some minor changes would be required in app.py, flask.Dockerfile and requirements.txt files)
+
+
+- Clone the repository and go to flask-backend folder. 
+- Build the docker image with following command:
+
+    `docker build -t flask-app -f flask.Dockerfile .`
+
+- Run the flask app with relevant environment variables using following command.
+
+    `docker run  -d --name flaskapp  -p 5000:5000  -e DB_HOST=<YOUR_DB_HOST_IP> -e DB_PORT=<YOUR_DB_PORT> -e DB_USER=<YOUR_DB_USER> -e DB_PASS=<YOUR_DB_PASSWORD> -e DB_NAME=<YOUR_DB_NAME> flask-app`
+
+
+- App should be up and running on http://localhost:5000/
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