README.md: add one more common mistake (#19436)

* README.md: add one more common mistake

* add article

* expanded the explanation a bit, added examples,

* wording

* s/better/more specific/

README.md

@@ -144,6 +144,7 @@ For a good example package, see [base64-js](https://github.com/DefinitelyTyped/D
     Example where a type parameter is acceptable: `function id<T>(value: T): T;`.
     Example where it is not acceptable: `function parseJson<T>(json: string): T;`.
     Exception: `new Map<string, number>()` is OK.
+* Using the types `Function` and `Object` is almost never a good idea. In 99% of cases it's possible to specify a more specific type. Examples are `(x: number) => number` for [functions](http://www.typescriptlang.org/docs/handbook/functions.html#function-types) and `{ x: number, y: number }` for objects. If there is no certainty at all about the type, [`any`](http://www.typescriptlang.org/docs/handbook/basic-types.html#any) is the right choice, not `Object`. If the only known fact about the type is that it's some object, use the type [`object`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-2.html#object-type), not `Object` or `{ [key: string]: any }`.
 
 
 #### Removing a package