webp-container-spec: clarify Chunk Size is in bytes
based on comments from:
@@ -123,8 +123,8 @@ Chunk FourCC: 32 bits
Chunk Size: 32 bits (_uint32_)
-: The size of the chunk not including this field, the chunk identifier or
- padding.
+: The size of the chunk in bytes, not including this field, the chunk
+ identifier or padding.
Chunk Payload: _Chunk Size_ bytes
