default subscriber for plottr does not work for its new version

[astafan8]

For implementing live plotting, the new plottr monitors the database file directly, without using the subscribers, hence the information in qcodes docs is not correct anymore.

See https://github.com/kouwenhovenlab/plottr/issues/36.

I suggest just to remove the mentioning of plottr, or substitute it with a link the exactly working version (which is now "the old plottr")

[Dominik-Vogel]

I agree - go for it! Monitoring the db file is really all it takes.

[jenshnielsen]

Plottr no longer uses subscriptions