Update debug logging section in the developer notes

doc/developer-notes.md

@@ -386,8 +386,10 @@ Run configure with the `--enable-gprof` option, then make.
 If the code is behaving strangely, take a look in the `debug.log` file in the data directory;
 error and debugging messages are written there.
 
-The `-debug=...` command-line option controls debugging; running with just `-debug` or `-debug=1` will turn
-on all categories (and give you a very large `debug.log` file).
+Debug logging can be enabled on startup with the `-debug` and `-loglevel`
+configuration options and toggled while bitcoind is running with the `logging`
+RPC.  For instance, launching bitcoind with `-debug` or `-debug=1` will turn on
+all log categories and `-loglevel=trace` will turn on all log severity levels.
 
 The Qt code routes `qDebug()` output to `debug.log` under category "qt": run with `-debug=qt`
 to see it.