Reemphasize that encoding lossy to lossless is useless

[FichteFoll]

I didn't like the wording suggested in #19 and @rokweom rightfully mentioned that we'd be repeating ourselves, so I propose a different solution that clarifies why you shouldn't reencode in the initial section and later references it for clarity.

[rokweom]

I feel like this is not really needed. If anything, we should make a separate section for explaining the difference between lossless and lossy, and explain why you should not encode from lossy to lossless there.

[FichteFoll]

Rebased and changed the wording slightly.