Added colab

Author: htahir1

docs/book/_config.yml

@@ -9,6 +9,8 @@ title                       : ZenML Docs  # The title of the book. Will be place
 author                      : maiot GmbH  # The author of the book
 copyright                   : "2021"  # Copyright year to be placed in the footer
 logo                        : logo.png  # A path to the book logo
+launch_buttons:
+  colab_url: "https://colab.research.google.com"
 repository:
   url: https://github.com/maiot-io/zenml
   path_to_book: docs/book