message: docs(README): corrected usage of articles
diff: @@ -24,7 +24,7 @@ class User {
  const UserModel = getModelForClass(User); // UserModel is a regular Mongoose Model with correct types
  (async () => {
  - await mongoose.connect('mongodb://localhost:27017/', { useNewUrlParser: true, useUnifiedTopology: true, dbName: "test" });
  + await mongoose.connect('mongodb://localhost:27017/', { useNewUrlParser: true, useUnifiedTopology: true, dbName: 'test' });
  const { _id: id } = await UserModel.create({ name: 'JohnDoe', jobs: ['Cleaner'] } as User); // an "as" assertion, to have types for all properties
  const user = await UserModel.findById(id).exec();
  @@ -44,7 +44,7 @@ Under the hood it uses the Reflect & [reflect-metadata](https://github.com/rbuck
  Instead of writing this:
  ```ts
  -// This is an representation of how typegoose's compile output would look like
  +// This is a representation of how typegoose's compile output would look like
  interface Car {
  model?: string;
  }
  @@ -105,22 +105,22 @@ class User {
  public name?: string;
  @prop({ required: true })
  - public age!: number; // This is an single Primitive
  + public age!: number; // This is a single Primitive
  @prop({ type: () => [String] })
  - public preferences?: string[]; // This is an Primitive Array
  + public preferences?: string[]; // This is a Primitive Array
  @prop()
  - public mainJob?: Job; // This is an single SubDocument
  + public mainJob?: Job; // This is a single SubDocument
  @prop({ type: () => Job })
  - public jobs?: Job[]; // This is an SubDocument Array
  + public jobs?: Job[]; // This is a SubDocument Array
  @prop({ ref: () => Car })
  - public mainCar?: Ref<Car>; // This is an single Reference
  + public mainCar?: Ref<Car>; // This is a single Reference
  @prop({ ref: () => Car })
  - public cars?: Ref<Car>[]; // This is an Reference Array
  + public cars?: Ref<Car>[]; // This is a Reference Array
  }
  ```
  