Add OpenStep to man page

docs/plistutil.1

diff --git a/docs/plistutil.1 b/docs/plistutil.1
index 64373b3..b2bf7bd 100644
--- a/docs/plistutil.1
+++ b/docs/plistutil.1
@@ -1,13 +1,13 @@
 .TH "plistutil" 1
 .SH NAME
-plistutil \- Convert a plist FILE between binary, XML, and JSON format
+plistutil \- Convert a plist FILE between binary, XML, JSON, and OpenStep formats
 .SH SYNOPSIS
 .B plistutil
 [OPTIONS]
 [-i FILE]
 [-o FILE]
 .SH DESCRIPTION
-plistutil allows converting a Property List file between binary, XML, and JSON format.
+plistutil allows converting a Property List file between binary, XML, JSON, and OpenStep formats.
 .SH OPTIONS
 .TP
 .B \-i, \-\-infile FILE