Be clear about what log_checkpoints emits in the documentation

Hi,

Currently the documentation of the log_checkpoints GUC says the following:

        Some statistics are included in the log messages, including the number
        of buffers written and the time spent writing them.

Usage of the word "Some" makes it a vague statement. Why can't we just
be clear about what statistics the log_checkpoints GUC can emit, like
the attached patch?

Thoughts?

Regards,
Bharath Rupireddy.