Update zoekt.md documentation

What does this merge request do and why?

We are getting the error with the current command:

[11] pry(main)> ApplicationSetting.current.update!(zoekt_settings: { zoekt_indexing_enabled: true, zoekt_indexing_paused: false, zoekt_search_enabled: true})
ActiveRecord::RecordInvalid: Validation failed: Zoekt cpu to tasks ratio is not a number
from /Users/ravikumar/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activerecord-7.0.8.4/lib/active_record/validations.rb:80:in `raise_validation_error'

After the change:

[15] pry(main)> ApplicationSetting.current.update!(zoekt_settings: { zoekt_indexing_enabled: true, zoekt_indexing_paused: false, zoekt_search_enabled: true, zoekt_cpu_to_tasks_ratio: 1.0})
=> true

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.