message: Doc the `env` setting in variants
diff: @@ -102,3 +102,10 @@ The option is itself a map with the following keys:
  A map of arbitrary CMake cache options to pass via the CMake command line
  with ``-D``. Similar to the ``cmake.configureSettings`` in
  ``settings.json``.
  +
  +``env``
  + A map of key-value string pairs specifying additional environment variables
  + to set during CMake *configure* (not build). These environment variables
  + take precedence over environment variables from ``settings.json``, the
  + currently set :ref:`kit <kits>`, and environment variables set by the
  + system.
  \ No newline at end of file
  