Add warning not to replace the whole osx folder

[vallezw]

Hey, thanks for the libraries! When I followed the instructions, I wanted to skip ahead and just pasted the whole osx folder from the zip file into Contents/MacOS. That replaced the whole osx folder and some other libraries went missing.

Maybe adding a little warning that one should not execute all steps at once would help.

[Ekaj1707]

I've edited & requested a commit to make this clearer, it's now on @AbeJellinek to merge it.