message: Explain how to import TimeStamps and Base defaultClasses
  defaultClasses(gh-page): add imports to the examples
  This is a squash merge of typegoose/typegoose#216
diff: @@ -15,19 +15,21 @@ This Guide contains all default classes typegoose provides
  Example of using all of them:
  ```ts
  +import { TimeStamps, Base } from '@typegoose/typegoose/lib/defaultClasses';
  +
  class SomeClass extends TimeStamps, Base {} // this class now has the types of "TimeStamps" & "Base"
  ```
  ### TimeStamps
  -The Time Stamps Class provides the following types:
  +The `TimeStamps` class provides the following fields:
  - `createdAt`: Date
  - `updatedAt`: Date
  ### Base
  -The Base Class provides the following types:
  +The Base Class provides the following fields:
  - `_id`: ObjectId
  - `__v`: number
  