Update README to include TACACS required configuration

[tchiapuziowong]

Issue to track README update to include TACACS option in CLI

https://community.arubanetworks.com/discussion/rest-api-error-when-trying-to-conenct-with-ansible

[alagoutte]

@tchiapuziowong do you want i write the PR ? (it is me write the first PR about add RADIUS info #36)

[tchiapuziowong]

@alagoutte sure! We appreciate the contribution!