document FRONTEND_CHECK_FOR_UPDATES

[Svanvith]

Please document how you can turn of the update checker in the webUI

opencloud-eu/web#1158

https://github.com/opencloud-eu/opencloud/pull/1556/files

I would place it under Admin -> Configuration

[Svanvith]

first draft frontend-check-for-updates
need to create screenshots

[tbsbdr]

@Svanvith missing screenshots can be added later, we should have this documented quickly.
do you have a link to the pr?

[Svanvith]

PR is not made because of missing screenshots ;) but I create one

[Svanvith]

@tbsbdr #521 now with screenshots ;)