Document how to secure the connection credentials

[idomic]

This is implemented but not well documented.
We should add a section about security best practices to tell the users how to pass their connection string in a secure way vs raw user/pass in their notebooks.

[edublancas]

agree: we should refactor this section - still contains the same docs as ipython-sql and replace it with best practices: one option is to use getpass, keyring is another option we can explain

[idomic]

@christophlingg @invisiblefunnel @AndreaCrotti @mottalrd @eshilts @tosolveit
We just updated the docs and released a new version( 0.5.2 changelog).
Make sure to join our slack for more info and support