In Active Record Querying guide, currently `Merging of scopes` section uses a concept of default scope in its example before it is introduced in the following section titled `Applying a default scope`.

It makes more sense to switch the ordering to introduce default scopes (`Applying a default scope`) first and then go into `Merging of scopes` section where it is used.
Merge pull request #14576 from ariabov/scope_sections_reordering

Change order of scope subsections in Active Record Querying guide [ci skip]