Let users choose between psycopg2 binary or source

doc/basic.rst

@@ -11,6 +11,20 @@ Please install django-redshift-backend with using pip (8.1.1 or later).
 
    $ pip install django-redshift-backend
 
+This backend requires ``psycopg2``, which may be installed from source or wheel (pre-built binaries).
+If you don't want to specify it separately, you may install it using extra:
+
+.. code-block:: bash
+
+   # For pre-built binary
+   $ pip install django-redshift-backend[psycopg2-binary]
+
+   # For the source distribution
+   $ pip install django-redshift-backend[psycopg2]
+
+Please refer to the `psycopg2 documentation`_ for more details on the topic.
+
+.. _psycopg2 documentation: https://www.psycopg.org/docs/install.html#psycopg-vs-psycopg-binary
 
 Django settings
 ===============
@@ -30,4 +44,3 @@ ENGINE for DATABASES is 'django_redshift_backend'. You can set the name in your
 
 For more information, please refer :doc:`refs`.
 
-

setup.py

@@ -3,7 +3,6 @@
 
 requires = [
     'django',
-    'psycopg2-binary',
 ]
 
 
@@ -25,6 +24,10 @@ def read(filename):
     description='Redshift database backend for Django',
     long_description=read('README.rst') + read('CHANGES.rst'),
     install_requires=requires,
+    extra_requires={
+        'psycopg2-binary': ['psycopg2-binary'],
+        'psycopg2': ['psycopg2'],
+    },
     python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*",
     classifiers=[
         'Development Status :: 5 - Production/Stable',