Manual: Query syntax is documented on closed corpus

Right now, all the examples in the `query.md` section of the manual are taken from the "Dutch Annual Reports" corpus. This documentation was originally made by José for the researchers of that project, but especially the section of examples with query / hits isn't very useful this way.

Alternatives:
- use an open (&English language?) corpus instead. E.g., Goodreads, or Parliament-Netherlands, if we're fine with Dutch examples
- ask if the "Dutch Annual Reports" (which is, contrary to the Dutch origin, English language) may be opened to everyone.

I suspect that option 2 wouldn't be met with much resistance, and would be less work.

Start with the query.md section of the manual and review the existing query and hits examples tied to the "Dutch Annual Reports" corpus. Determine whether an open corpus can replace it or whether access to that corpus can be opened; done means the examples use a corpus available to the intended readers and the manual reflects that choice.

Written by the indexing model from the issue text.