Document new -e flag

sxiv.1

@@ -4,6 +4,8 @@ sxiv \- Simple X Image Viewer
 .SH SYNOPSIS
 .B sxiv
 .RB [ \-abcfhioqrtvZ ]
+.RB [ \-e
+.IR WID ]
 .RB [ \-G
 .IR GAMMA ]
 .RB [ \-g
@@ -40,6 +42,10 @@ Do not show info bar on bottom of window.
 .B \-c
 Remove all orphaned cache files from the thumbnail cache directory and exit.
 .TP
+.BI "\-e " WID
+Embed sxiv's window into window whose ID is
+.IR WID .
+.TP
 .B \-f
 Start in fullscreen mode.
 .TP