Update readme

Hello,

I've just had an attempt at updating (and also attempting to simplify where possible) the readme file to try reflect the updated file structure, as well as some of the new  features available (such as the `makelinks.sh`). I also removed the "EXISTING RES CONTRIBUTORS" note at the top on the assumption that more a less everyone who would need to see it hopefully have by now, although i can re-add if its still seen as useful.

Demo: https://github.com/thybag/Reddit-Enhancement-Suite/tree/feature/update-readme

fixes: https://github.com/honestbleeps/Reddit-Enhancement-Suite/issues/780