More standardish usage info in man page

sxiv.1

@@ -4,7 +4,7 @@ sxiv \- Simple (or small or suckless) X Image Viewer
 .SH SYNOPSIS
 .B sxiv
 .RB [ \-hv ]
-.B FILES...
+.IR FILE ...
 .SH DESCRIPTION
 sxiv is a simple image viewer for X. It only has the most basic features
 required for fast image viewing.