describe correct option names in xcam man page

doc/xcam.man

@@ -4,7 +4,7 @@
 xcam - a graphical camera frontend for SANE
 .SH SYNOPSIS
 .B xcam
-.RB [ --buffer | -B  ]
+.RB [ --buffersize | -B  ]
 .RB [ --version | -V ]
 .RB [ --help | -h ]
 
@@ -30,7 +30,7 @@ presents a menu listing of all known and available devices.
 .SH OPTIONS
 .PP
 If the
-.B --Buffer (-B)
+.B --buffersize (-B)
 option is given,
 .B xcam 
 will use a 1024 kByte input buffer instead of the default 32 kByte.