either bridge foolscap log messages to twistd.log, or remove the section of logging.rst about that

[davidsarah]

From git/docs/logging.rst@959248cd

Local twistd.log files
======================

[TODO: not yet true, requires foolscap-0.3.1 and a change to ``allmydata.node``]

In addition to the foolscap-based event logs, certain high-level events will
be recorded directly in human-readable text form, in the
``BASEDIR/logs/twistd.log`` file (and its rotated old versions:
``twistd.log.1``, ``twistd.log.2``, etc). This form does not contain as much
information as the flogfiles available through the means described
previously, but they are immediately available to the curious developer, and
are retained until the twistd.log.NN files are explicitly deleted.

Only events at the ``log.OPERATIONAL`` level or higher are bridged to
``twistd.log`` (i.e. not the ``log.NOISY`` debugging events). In addition,
foolscap internal events (like connection negotiation messages) are not
bridged to ``twistd.log``.

[davidsarah]

I'm not sure the threshold should be >= log.OPERATIONAL though; that's possibly a bit too verbose. Maybe > log.OPERATIONAL ?