Add sentinel auth to an exemple in the documentation.

[Christophe31]

Problem Statement
django-redis seems to be the best way to add sentinel feature of redis to django cache… the authentication is unclear to add and seems undocumented.

Describe the solution you'd like
either use the "PASSWORD" for sentinel connection, or add authenticated sentinel params to the README

ex: #610

[WisdomPill]

thanks @Christophe31 for raising the issue? would you like to open a PR to fix the issue?