message: Mention default variants in the docs
diff: @@ -77,6 +77,9 @@ command from the command palette. A quick-pick will appear:
  The active build variant will be displayed on the same statusbar button, along
  with the project name and extension status.
  +CMake Tools will load up the default variant when it doesn't detect a prior
  +selection. For the default variant, this will be ``Debug``.
  +
  Find out more on the :ref:`variants` page.
  Running Configuration
  