message: docs(prop): add default function example
diff: @@ -73,6 +73,22 @@ class Defaulted {
  }
  ```
  +You may also set the `default` schema option to a function. Mongoose will execute that function and use the return value as the default.
  +
  +Example:
  +
  +```ts
  +class Defaulted {
  + @prop({
  + default: (this: DocumentType<Defaulted>) => {
  + return `${this.firstName} ${this.lastName}`
  + }
  + })
  + public fullName?: string; // mark as optional, because it will be defaulted
  +}
  +```
  +Note: to have the `this` keyword correctly typed, you have to pass a [this parameter](https://www.typescriptlang.org/docs/handbook/functions.html#this-parameters).
  +
  ### _id
  Accepts Type: `boolean`
  