Add extras for optional requirements

AUTHORS

@@ -3,4 +3,5 @@ Gilles Fabio
 Jannis Leidel
 Marc Abramowitz
 Michael van Tellingen
-Mike Fogel
+Mike Fogel
+Peter Bittner

README.rst

@@ -32,6 +32,12 @@ Install django-configurations:
 
     pip install django-configurations
 
+or, alternatively, if you want to use URL-based values:
+
+.. code-block:: console
+
+    pip install django-configurations[cache,database,email,search]
+
 Then subclass the included ``configurations.Configuration`` class in your
 project's **settings.py** or any other module you're using to store the
 settings constants, e.g.:

setup.py

@@ -41,6 +41,12 @@ setup(
             'django-cadmin = configurations.management:execute_from_command_line',
         ],
     },
+    extras_require={
+        'cache': ['django-cache-url'],
+        'database': ['dj-database-url'],
+        'email': ['dj-email-url'],
+        'search': ['dj-search-url'],
+    },
     classifiers=[
         'Development Status :: 5 - Production/Stable',
         'Framework :: Django',