fix docs to include -f video4linux

ffmpeg2theora.1

@@ -212,7 +212,7 @@ Encode a series of images:
   ffmpeg2theora frame%06d.png -o output.ogv
 
 Live streaming from V4L Device:
-  ffmpeg2theora /dev/video0 \-\-inputfps 15 \-x 160 \-y 128 \-o \- \\
+  ffmpeg2theora /dev/video0 \-f video4linux \-\-inputfps 15 \-x 160 \-y 128 \-o \- \\
     | oggfwd iccast2server 8000 password /theora.ogv
 
 Live encoding from a DV camcorder (needs a fast machine):

src/ffmpeg2theora.c

@@ -1209,7 +1209,7 @@ void print_usage (){
         "    ffmpeg2theora frame%%06d.png -o output.ogv\n"
         "\n"
         "  Live streaming from V4L Device:\n"
-        "    ffmpeg2theora /dev/video0 -fps 15 -x 160 -y 128 -o - \\\n"
+        "    ffmpeg2theora /dev/video0 -f video4linux -fps 15 -x 160 -y 128 -o - \\\n"
         "     | oggfwd iccast2server 8000 password /theora.ogv\n"
         "\n"
         "  Live encoding from a DV camcorder (needs a fast machine):\n"