message: Explain the difference between ref: Class and ref: 'Class'
  prop(gh-page): explain the difference between ref: Class and ref: 'Class'
  This is a squash merge of typegoose/typegoose#280
diff: @@ -106,11 +106,14 @@ class Parent {
  @prop({ ref: Nested })
  public nest: Ref<Nested>;
  // or
  - @prop({ ref: "Nested" })
  + @prop({ ref: 'Nested' })
  public nest: Ref<Nested>;
  }
  ```
  +The `'Nested'` form is useful to avoid unintuitive errors due to circular dependencies, such as
  +`Error: Options "ref" is set, but is undefined/null!`.
  +
  ### refPath
  Accepts Type: `string`
  