fix(doc) mention video support in exiv2.md

Author: hassec

exiv2.md

@@ -116,6 +116,10 @@ and see if `enable_bmff=1`.
 
 - Naked codestream JXL files do not contain Exif, IPTC or XMP metadata.
 
+- Support of video files is limited. Currently **exiv2** only has some
+  rudimentary support to read metadata from quicktime based video files (e.g.
+  .MOV/.MP4).
+
 
 [TOC](#TOC)