Update MultiFormatReader example in README.md

[inokawa]

If we call decode of MultiFormatReader without hints argument, this.hints seems overrided with undefined.

library/src/core/MultiFormatReader.ts

Lines 72 to 75 in 89c4c23

	public decode(image: BinaryBitmap, hints?: Map<DecodeHintType, any>): Result {
	this.setHints(hints);
	return this.decodeInternal(image);
	}

library/src/core/MultiFormatReader.ts

Lines 101 to 102 in 89c4c23

	public setHints(hints?: Map<DecodeHintType, any> | null): void {
	this.hints = hints;