message: Update swagger-extensions.md
diff: @@ -361,6 +361,7 @@ It can be used for query parameters and header parameters, as well as properties
  }
  }
  ```
  +
  ## x-ms-external
  To allow generated clients to share models via shared libraries an `x-ms-external` extension was introduced. When a [Definition Objects](https://github.com/swagger-api/swagger-spec/blob/master/versions/2.0.md#definitionsObject) contains this extensions it's definition will be excluded from generated library. Note that in strongly typed languages the code will not compile unless the assembly containing the type is referenced with the project/library.
  @@ -405,6 +406,7 @@ Swagger 2.0 specification requires that when used, the value of `discriminator`
  }
  }
  ```
  +
  ## x-ms-client-flatten
  This extension allows to flatten deeply nested payloads into a more user friendly object. For example a payload that looks like this on the wire:
  ```js
  