Documentation: Fix incorrect range for near-lossless compression

[joppuyo]

On the "near-lossless" option, the documentation says the range is 0 (no preprocessing) to 100 (maximum preprocessing) so I set it to 0. Then I started wondering why all my WebPs look so blurry even if they are supposed to be lossless. 😅

Turns out there was a typo with this particular documentation, the real range is 0 (maximum preprocessing) to 100 (no preprocessing), per WebP documentation.

There's another mention of the option here but the range is the right way around in that instance.

[joppuyo]

Found another reference to the near-lossless option where the range is wrong. I'm not sure where the text is visible, but I fixed it anyway.

[rosell-dk]

thanks!