avformat: update AVInputFormat allowed flags

libavformat/avformat.h

@@ -406,7 +406,9 @@ typedef struct AVInputFormat {
                               int64_t *pos, int64_t pos_limit);
 
     /**
-     * Can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER.
+     * Can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER, AVFMT_SHOW_IDS,
+     * AVFMT_GENERIC_INDEX, AVFMT_TS_DISCONT, AVFMT_NOBINSEARCH,
+     * AVFMT_NOGENSEARCH.
      */
     int flags;