Update man-page for v0.5

Makefile

@@ -5,7 +5,7 @@ mandir = $(PREFIX)/share/man/man1
 PKG_CONFIG ?= pkg-config
 CXXFLAGS ?= -Wall -O3 -ffast-math
 
-VERSION?=$(shell (git describe --tags HEAD 2>/dev/null || echo "v0.4") | sed 's/^v//')
+VERSION?=$(shell (git describe --tags HEAD 2>/dev/null || echo "v0.5") | sed 's/^v//')
 
 ###############################################################################
 

sound-gambit.1

@@ -1,5 +1,5 @@
 .\" DO NOT MODIFY THIS FILE!  It was generated by help2man 1.48.1.
-.TH SOUND-GAMBIT "1" "March 2021" "sound-gambit version 0.4" "User Commands"
+.TH SOUND-GAMBIT "1" "March 2021" "sound-gambit version 0.5" "User Commands"
 .SH NAME
 sound-gambit \- Audio File Peak Limiter
 .SH SYNOPSIS
@@ -9,6 +9,9 @@ sound-gambit \- Audio File Peak Limiter
 sound\-gambit \- an Audio File Digital Peak Limiter.
 .SH OPTIONS
 .TP
+\fB\-a\fR, \fB\-\-auto\-gain\fR
+specify gain relative to peak
+.TP
 \fB\-i\fR, \fB\-\-input\-gain\fR <db>
 input gain in dB (default 0)
 .TP
@@ -42,6 +45,10 @@ Reading via standard\-I/O is supported, use '\-' as file\-name.
 Prior to processing, additional input\-gain can be applied. The allowed
 range is \fB\-10\fR to +30 dB.
 .PP
+When auto\-gain is enabled, input\-gain is relative to the given threshold,
+and specifies the amount of effective gain\-reduction to be applied.
+If input\-gain is zero, the file is only normalized to the given threshold.
+.PP
 The threshold range is \fB\-10\fR to 0 dBFS, and the limiter will not allow a
 single sample above this level.
 .PP