Add default logging config example

As requested in review, this begins by documenting how to replicate
NAV's default logging config, and proceeds to document Humio only after
that.

doc/howto/setting-up-logging.rst

@@ -137,11 +137,50 @@ extensive knowledge of how the standard Python logging framework works.
 and parsed.  This means that :file:`logging.yml` must adhere to the
 configuration dictionary schema laid out in the Python docs.
 
-This can allow you to do such things as sending all NAV log records to a Falcon
-LogScale (previously known as Humio) ingestor using something like the
-`humiologging <https://pypi.org/project/humiologging/>`_ library.  Instead of
-shipping the file-based logs to LogScale and having them parsed there, each log
-record can be shipped with structured attributes/tags.
+Be aware that by adding configuration to :file:`logging.yml`, you are altering
+NAV's default logging configuration at a very low level, and you may also be
+altering NAV's default behavior of storing logs in files. A :file:`logging.yml`
+that replicates a default NAV setup may look something like this:
+
+.. code-block:: yaml
+
+   version: 1
+   loggers:
+     nav:
+       level: INFO
+     root:
+       handlers: [console]
+
+   formatters:
+     default:
+       format: '%(asctime)s [%(levelname)s] [%(name)s] %(message)s'
+
+   handlers:
+     console:
+       class: logging.StreamHandler
+       formatter: default
+
+This replicates a setup that logs only **INFO**-level messages and above from
+NAV to ``stderr``, using NAV's default log message format.  Individual NAV
+daemons will redirect their ``stderr`` streams to their respective log files as
+they fork off background processes, so there is no need to redefine these.
+
+Leaving out the :class:`logging.StreamHandler` will still cause the log files
+to be created, but they will be empty (save for any outpout to ``stderr`` that
+did not come from the :mod:`logging` library).
+
+.. tip:: As with :file:`logging.conf`, processes can be directed to read a
+         bespoke :file:`logging.yml` file, but by setting the
+         :envvar:`NAV_LOGGING_YML` environment variable instead.
+
+Example: Directing logs to Falcon LogScale (Humio)
+--------------------------------------------------
+
+The following example shows how you can make all NAV programs ship their log
+messages to a Falcon LogScale (previously known as Humio) ingestor using
+something like the `humiologging <https://pypi.org/project/humiologging/>`_
+library.  Instead of shipping the file-based logs to LogScale and having them
+parsed there, each log record can be shipped with structured attributes/tags.
 
 To achieve something like this, you need to first install the
 :mod:`humiologging` library into your NAV installation's Python environment
@@ -158,6 +197,10 @@ similar to this:
      root:
        handlers: [humio, console]
 
+   formatters:
+     default:
+       format: '%(asctime)s [%(levelname)s] [%(name)s] %(message)s'
+
    handlers:
      humio:
        class: humiologging.handlers.HumioJSONHandler
@@ -169,25 +212,11 @@ similar to this:
        formatter: default
 
 
-   formatters:
-     default:
-       format: '%(asctime)s [%(levelname)s] [%(name)s] %(message)s'
-
 This configuration attaches a :class:`HumioJSONHandler` to the ``root`` logger
 and sets the global NAV log level to **DEBUG**.  Unfortunately, as this
 configuration manipulates the ``root`` logger, it removes the handler(s) that
 NAV has by default installed on it, so if you want NAV to also keep logging to
-files in addition to Humio, you need to add an extra handler that logs to a
-stream (``stderr`` by default), and you need to specify a format for it.  This
-example just redefines the log line format NAV uses by default.
+files in addition to Humio, you need to replicate parts of NAV's default setup,
+as mentioned in the previous section.  Add an extra handler named ``console``
+that logs to a stream (``stderr`` by default), and specify a format for it.
 
-As long as you add a :class:`logging.StreamHandler` to ``root``, you shouldn't
-need to redefine which files the logs go to, as most NAV daemons achieve this
-by redirecting their ``stderr`` to a file as they fork off a background
-process.  Leaving out the :class:`logging.StreamHandler` will still cause the
-log files to be created, but they will be empty (save for any outpout to
-``stderr`` that did not come from the :mod:`logging` library).
-
-.. tip:: As with :file:`logging.conf`, processes can be directed to read a
-         bespoke :file:`logging.yml` file, but by setting the
-         :envvar:`NAV_LOGGING_YML` environment variable instead.