message: add note about docs
diff: * 0.6.12
  +* [Botkit has a brand new docs site!](https://botkit.ai/docs) We have begun transitioning the documentation out of this repo into a [dedicated documentation repo](https://github.com/howdyai/botkit-docs).
  +
  * Remove dependency on Python introduced in 0.6.10. Thanks to @qiongfangzhang for the attention on that!
  * Fix for Facebook Messenger send broadcast function. [PR #1280](https://github.com/howdyai/botkit/pull/1280) Thanks @OmranAbazid
  