docs: Connecting to local database when using Superset docker image

[rukshn]

SUMMARY

When using superset docker image, connecting to a local database using 127.0.0.1 or localhost as the database hose does not work and throws the following error. https://docs.sqlalchemy.org/en/14/errors.html#error-e3q8

The correct host address should be 172.18.0.1 instead of localhost or 127.0.0.1 as written in the superset documentation on this page - https://superset.apache.org/docs/installation/installing-superset-using-docker-compose#5-connecting-superset-to-your-local-database-instance