docs: more examples

[chendaniely]

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