open( my $makefile, '<', $0) or die "Could not open $0: $!\n";
$_ = do {local $/; <$makefile>};

if (($_) = m#PREREQ_PM\s*=>\s*{([^}]+)}#) {
    my @module = map {s#['"]##g; $_} m#(\S+)\s*=>#sg;
    open( my $readme, '<', 'README' ) or die "Could not open README: $!\n";
    $_ = do {local $/; <$readme>};
    if (s#(\nRequired Modules:\n)(?:.*?)(\n\n)#"$1  ".(do {local $"="\n  ","@module"}).$2#se) {
        open( $readme, '>', 'README' ) or die "Could not open README: $!\n";
        print $readme $_;
    }
}