example-config: Add log_debug and log_core_filter

doc/example-config/conf.d/10-logging.conf

@@ -20,6 +20,26 @@
 ## Logging verbosity and debugging.
 ##
 
+# Log filter is a space-separated list conditions. If any of the conditions
+# match, the log filter matches (i.e. they're ORed together). Parenthesis
+# are supported if multiple conditions need to be matched together.
+# Supported conditions are:
+#  event:<name wildcard> - Match event name. '*' and '?' wildcards supported.
+#  source:<filename>[:<line number>] - Match source code filename [and line]
+#  field:<key>=<value wildcard> - Match field key to a value. Can be specified
+#    multiple times to match multiple keys.
+#  cat[egory]:<value> - Match a category. Can be specified multiple times to
+#    match multiple categories.
+# For example: event:http_request_* (cat:error cat:storage)
+
+# Filter to specify what debug logging to enable. This will eventually replace
+# mail_debug and auth_debug settings.
+#log_debug = 
+
+# Crash after logging a matching event. For example category:error will crash
+# any time an error is logged, which can be useful for debugging.
+#log_core_filter = 
+
 # Log unsuccessful authentication attempts and the reasons why they failed.
 #auth_verbose = no