[DOC beta] Clarified sort description

sort() is comparing comparator result being >0 or <0, it does not depend on strict 1 or -1. With original documentation people wanting to comply with specification they need to do if( a === b ) { return 0; } else { if( a > b ) { return -1; } else { return 1; } instead of simple subtraction.
Merge pull request #4406 from Nopik/master

Clarified sort description