doc: Fix syntax and logical errors in avconv stream combination example

Bug-Id: 661
CC: libav-stable@libav.org

doc/avconv.texi

@@ -1129,11 +1129,11 @@ only formats accepting a normal integer are suitable.
 You can put many streams of the same type in the output:
 
 @example
-avconv -i test1.avi -i test2.avi -map 0.3 -map 0.2 -map 0.1 -map 0.0 -c copy test12.nut
+avconv -i test1.avi -i test2.avi -map 1:1 -map 1:0 -map 0:1 -map 0:0 -c copy -y test12.nut
 @end example
 
-The resulting output file @file{test12.avi} will contain first four streams from
-the input file in reverse order.
+The resulting output file @file{test12.nut} will contain the first four streams
+from the input files in reverse order.
 
 @item
 To force CBR video output: