Add warning about managing multiple versions with pipenv (pypa#430)

* Add warning about managing multiple versions with pipenv

* Provide additional details on the version problem

Author: Jon Wayne Parrott

source/tutorials/managing-dependencies.rst

@@ -24,7 +24,6 @@ testing environments for any kind of project.
 .. Note:: This guide is written for Python 3, however, these instructions
     should also work on Python 2.7.
 
-
 Installing Pipenv
 -----------------
 
@@ -114,7 +113,17 @@ when you share your project with others. You should get output similar to this
     Adding requests to Pipfile's [packages]...
     P.S. You have excellent taste! ✨ 🍰 ✨
 
+.. Warning:: Due to an `open issue with pipenv`_, it's not currently reliable
+    to use ``pipenv`` to create environments for different Python versions
+    (as environment marker conditions may not be processed correctly).
+    The interpreter version you use in your project should be the same as the
+    interpreter version used to install ``pipenv``.
+    When testing against multiple versions with ``tox``, install ``pipenv``
+    into each test environment, as described `here <pipenv-tox>`_.
+
 .. _Requests: https://python-requests.org
+.. _open issue with pipenv: https://github.com/pypa/pipenv/issues/857
+.. _pipenv-tox: https://docs.pipenv.org/advanced/#tox-automation-project
 
 
 Using installed packages