std/vp8: add README.md

std/vp8/README.md

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+# VP8
+
+VP8 is a compressed video data format, described in [RFC
+6386](https://www.ietf.org/rfc/rfc6386.txt).
+
+The WebM movie (moving image) format consists of muliple VP8 frames, both key
+(I-Frames) and non-key (B-Frames, P-Frames, etc). Separate from WebM, the WebP
+still image format essentially wraps one VP8 key frame.

std/webp/README.md

diff --git a/std/webp/README.md b/std/webp/README.md
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 # WebP
 
-WebP is a still image format, described in [RFC
-6386](https://www.ietf.org/rfc/rfc6386.txt).
+WebP is a still image format, described in the [WebP Container
+Specification](https://developers.google.com/speed/webp/docs/riff_container).
 
 The ["Making Software - Image
 Compression"](https://www.makingsoftware.com/chapters/image-compression) book
 chapter also has a good overview of a number of image formats, including WebP.
 
-There are two WebP variants: lossy (based on VP8) and lossless. Wuffs' VP8
+There are two WebP variants: lossy (based on VP8) and lossless (based on what's
+essentially an unrelated design, other than "WebP" branding). Wuffs' VP8
 implementation is in a separate package, as the WebM moving image format also
 uses VP8. There's no Wuffs WebM package yet but there might be in the future.