message: Fix the WebP spelling in README
diff: @@ -26,7 +26,7 @@ https://docs.rs/image
  | BMP | Yes | RGB(8), RGBA(8), Gray(8), GrayA(8) |
  | ICO | Yes | Yes |
  | TIFF | Baseline(no fax support) + LZW + PackBits | RGB(8), RGBA(8), Gray(8) |
  -| Webp | Lossy(Luma channel only) | No |
  +| WebP | Lossy(Luma channel only) | No |
  | PNM | PBM, PGM, PPM, standard PAM | Yes |
  ### 2.2 The ```ImageDecoder``` Trait
  