qt-faststart: Add a note about the -movflags +faststart feature

Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 700687ebe0)

tools/qt-faststart.c

@@ -102,7 +102,8 @@ int main(int argc, char *argv[])
     int bytes_to_copy;
 
     if (argc != 3) {
-        printf("Usage: qt-faststart <infile.mov> <outfile.mov>\n");
+        printf("Usage: qt-faststart <infile.mov> <outfile.mov>\n"
+               "Note: alternatively you can use -movflags +faststart in avconv\n");
         return 0;
     }