Ref to build environment

Author: stsewd

docs/config-file/v2.rst

@@ -139,6 +139,10 @@ Give the virtual environment access to the global site-packages directory.
 :Type: ``bool``
 :Default: ``false``
 
+Depending on the :ref:`config-file/v2:build.image`,
+Read the Docs includes some libraries like scipy, numpy, etc.
+See :ref:`builds:The build environment` for more details. 
+
 conda
 ~~~~~