Document connecting to Redis via TLS

[p4block]

Proposal

Add an example of connection to Redis via TLS

Motivation and context

I needed to connect to a DigitalOcean managed Redis, they use TLS. Viewing the config.php I saw that you could give the tls value to the SCHEME field.

PCA_REDIS_0_SCHEME: tls

This is not clear in the current README

[RobiNN1]

I thought "connection scheme" was an obvious name. The same name for this option is used in any other library/framework as well. E.g. in Laravel.

In config tls it's only as an example and also this option is usually used for tls connection since default is tcp. You can use any scheme supported by Redis.