message: Added documentation for index option in prop decorator
diff: @@ -152,10 +152,23 @@ firstName: string;
  // by default, a property is not required
  @prop()
  lastName?: string; // using the ? optional property
  +```
  +
  + - `index`: Tells Mongoose whether to define an index for the property.
  +
  +```typescript
  +@prop({ index: true })
  +indexedField?: string;
  ```
  - `unique`: Just like the [Mongoose unique](http://mongoosejs.com/docs/api.html#schematype_SchemaType-unique), tells Mongoose to ensure a unique index is created for this path.
  +```typescript
  +// this field is now unique across the collection
  +@prop({ unique: true })
  +uniqueId?: string;
  +```
  +
  ```typescript
  // this field is now unique across the collection
  @prop({ unique: true })
  