docs: more examples

From PR #19:

TODO:

- [ ]  create more examples with different database engines (e.g., snowflake, databricks, etc)
- [ ]  for snowflake use the user:pass string, but also show example for using snowflake.connector.connect
- [ ]  Check readme for new api changes that take dataframe or sqlalchemy connection
- [ ]  Check readme for new api changes of returning a querychat object not dict