Update documentation for drush commands on website and in readme

I updated documentation, this going to be changed again in 2.0.

Automatically closed - issue fixed for 2 weeks with no activity.

README in version 8.x-1.2 still has the following commands that no longer work in Drupal 9 or 10.
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Check the status: drush vget site_readonly
Turn on Read Only Mode: drush vset site_readonly 1
Turn off Read Only Mode: drush vset site_readonly 0
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Following commands suggested in this post do not work either:

drush config:set readonlymode.settings site_readonly 1 (to enable)
drush config:set readonlymode.settings site_readonly 0 (to disable)

I get this when I try to run them:

site_readonly key does not exist in readonlymode.settings config. Do you want to create a new config key? (yes/no) [yes]:

The following drush commands work fine with 2.0.x-dev version installed:

Check the status: `drush state:get readonlymode_active`
Turn on Read Only Mode: `drush state:set readonlymode_active 1`
Turn off Read Only Mode: `drush state:delete readonlymode_active`