mpdconf.example: improve documentation for replay gain

- Added replaygain_missing_preamp and replaygain_limit settings

- Added information about "auto" replay gain mode

doc/mpdconf.example

@@ -321,8 +321,11 @@ input {
 # Normalization automatic volume adjustments ##################################
 #
 # This setting specifies the type of ReplayGain to use. This setting can have
-# the argument "off", "album" or "track". See <http://www.replaygain.org>
-# for more details. This setting is off by default.
+# the argument "off", "album", "track" or "auto". "auto" is a special mode that
+# chooses between "track" and "album" depending on the current state of
+# random playback. If random playback is enabled then "track" mode is used.
+# See <http://www.replaygain.org> for more details about ReplayGain.
+# This setting is off by default.
 #
 #replaygain			"album"
 #
@@ -331,6 +334,20 @@ input {
 #
 #replaygain_preamp		"0"
 #
+# This setting sets the pre-amp used for files that do NOT have ReplayGain tags.
+# By default this setting is disabled.
+#
+#replaygain_missing_preamp	"0"
+#
+# This setting enables or disables ReplayGain limiting.
+# MPD calculates actual amplification based on the ReplayGain tags
+# and replaygain_preamp / replaygain_missing_preamp setting.
+# If replaygain_limit is enabled MPD will never amplify audio signal
+# above its original level. If replaygain_limit is disabled such amplification
+# might occur. By default this setting is enabled.
+#
+#replaygain_limit		"yes"
+#
 # This setting enables on-the-fly normalization volume adjustment. This will
 # result in the volume of all playing audio to be adjusted so the output has 
 # equal "loudness". This setting is disabled by default.