lavc/options_table: Add option flags to the truncated flag.

Also add a short description for the help output.

libavcodec/options_table.h

@@ -70,7 +70,7 @@ static const AVOption avcodec_options[] = {
 {"emu_edge", "do not draw edges", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_EMU_EDGE }, INT_MIN, INT_MAX, 0, "flags"},
 #endif
 {"psnr", "error[?] variables will be set during encoding", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_PSNR }, INT_MIN, INT_MAX, V|E, "flags"},
-{"truncated", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_TRUNCATED }, INT_MIN, INT_MAX, 0, "flags"},
+{"truncated", "Input bitstream might be randomly truncated", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_TRUNCATED }, INT_MIN, INT_MAX, V|D, "flags"},
 #if FF_API_NORMALIZE_AQP
 {"naq", "normalize adaptive quantization", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_NORMALIZE_AQP }, INT_MIN, INT_MAX, V|E, "flags"},
 #endif