Fix README typos

[inhibitor1217]

Spotted some typos in the code and plain text.. should fix them

[inhibitor1217]

Matches

extended enumerations provide a default method named is. is is aware of the primitives defining the enumeration.

enum _Fruit {
  Apple = 'APPLE',
  Orange = 'ORANGE',
}
const Fruit = extend<typeof _Fruit, Fruit>(Fruit);

const Fruit = extend<typeof _Fruit, Fruit>(Fruit); should be const Fruit = extend<typeof _Fruit, _Fruit>(_Fruit);

[inhibitor1217]

The exhuastive typing of union is not supported yet

should be

The exhaustive typing of union is not supported yet

[jirheee]

I think there is a typo at what-powers-does-it-have.

expect(Animal.Cat !== Animal.Dog).toBe(false);

I think this should be corrected to either one of below, if it was supposed to describe that extended enum works like original TS enums when the are compared.

expect(Animal.Cat !== Animal.Cat).toBe(false);

expect(Animal.Cat !== Animal.Dog).toBe(true);

expect(Animal.Cat === Animal.Dog).toBe(false);

[inhibitor1217]

Typos until this comment are corrected in #40. Please comment any existing typos in README.md in this issue. :+1: