DOC: Improve install instructions in README.rst

The README now notes the current supported Python versions, and refers
the reader to zipline.io for details. (The README's details had become
out of sync with zipline.io, which also needs to be redeployed to
bring in some recent changes.)

Resolves #2571.

Author: quantophred

README.rst

@@ -40,62 +40,15 @@ Features
 Installation
 ============
 
-Installing With ``pip``
------------------------
+Zipline currently supports Python 2.7 and Python 3.5, and may be installed via
+either pip or conda.
 
-Assuming you have all required (see note below) non-Python dependencies, you
-can install Zipline with ``pip`` via:
+**Note:** Installing Zipline is slightly more involved than the average Python
+package. See the full `Zipline Install Documentation`_ for detailed
+instructions.
 
-.. code-block:: bash
-
-    $ pip install zipline
-
-**Note:** Installing Zipline via ``pip`` is slightly more involved than the
-average Python package.  Simply running ``pip install zipline`` will likely
-fail if you've never installed any scientific Python packages before.
-
-There are two reasons for the additional complexity:
-
-1. Zipline ships several C extensions that require access to the CPython C API.
-   In order to build the C extensions, ``pip`` needs access to the CPython
-   header files for your Python installation.
-
-2. Zipline depends on `numpy <https://www.numpy.org/>`_, the core library for
-   numerical array computing in Python.  Numpy depends on having the `LAPACK
-   <https://www.netlib.org/lapack/>`_ linear algebra routines available.
-
-Because LAPACK and the CPython headers are binary dependencies, the correct way
-to install them varies from platform to platform.  On Linux, users generally
-acquire these dependencies via a package manager like ``apt``, ``yum``, or
-``pacman``.  On OSX, `Homebrew <https://brew.sh/>`_ is a popular choice
-providing similar functionality.
-
-See the full `Zipline Install Documentation`_ for more information on acquiring
-binary dependencies for your specific platform.
-
-conda
------
-
-Another way to install Zipline is via the ``conda`` package manager, which
-comes as part of `Anaconda <https://www.anaconda.com/distribution/>`_ or can be
-installed via ``pip install conda``.
-
-Once set up, you can install Zipline from our ``Quantopian`` channel:
-
-.. code-block:: bash
-
-    $ conda install -c Quantopian zipline
-
-Currently supported platforms include:
-
--  GNU/Linux 64-bit
--  OSX 64-bit
--  Windows 64-bit
-
-.. note::
-
-   Windows 32-bit may work; however, it is not currently included in
-   continuous integration tests.
+For a development installation (used to develop Zipline itself), create and
+activate a virtualenv, then run the ``etc/dev-install`` script.
 
 Quickstart
 ==========