List minimum SDL versions for satellite libraries

[icculus]

This is probably something for the wiki.

SDL3_image version	SDL3 version
3.2.x	3.2.x
3.4.x	3.4.x

SDL3_mixer version	SDL3 version
3.2.x	3.4.x

SDL3_ttf version	SDL3 version
3.2.x	3.2.x

SDL3_net version	SDL3 version
3.2.x	TBD

Originally posted by @madebr in #848

Just decide on a page for this, or if these should just be in every library README, or both.