Updated Readme for BigInt 4.0, removed paragraph about "Full-width multiplication and division primitives", which explained implementation details of BigInt 2.0.
Updated Readme for BigInt 4.0, removed paragraph about "Full-width multiplication and division primitives", which explained implementation details of BigInt 2.0.

attaswift/BigInt,lorentey/BigInt,attaswift/BigInt,lorentey/BigInt