Instructions use currentbackup while the command is deprecated

[the-Jamz]

As stated here the currentbackup command is deprecated given the implementation of archive_timeout, but no alternative instructions are given unless you dig through commit messages.

At least, the practice section of the readme can be updated to explain this, and if you guys would like I can put together a PR to configure archive_timeout to 60s on setup, as was recommended to do previously with a cronjob and currentbackup.