Redis requirement missing from Readme.md

I see this error in the Apache logs when I press "[RE]LOAD SERVICE" button of Push for Nextcloud android app.

Nextcloud/SSEPush: Redis is not installed.

I looked at the source code and it tries to connect to redis. I didn't know it was a requirement. I also noticed under Administration -> Mobile Push Messages it says "1) This service required Redis to be installed and configured for use by Nextcloud. The database ID used will be 1 higher than the database ID used by Nextcloud."