Add Sphinx as an extra requirement to 'setup.py'

setup.py

@@ -2,7 +2,6 @@ from os.path import dirname, realpath, join
 
 from setuptools import setup, find_packages
 
-
 here = dirname(realpath(__file__))
 
 with open(join(here, 'VERSION'), 'r') as ifile:
@@ -10,7 +9,8 @@ with open(join(here, 'VERSION'), 'r') as ifile:
 with open(join(here, 'requirements.txt'), 'r') as ifile:
     requirements = ifile.read().splitlines()
 
-setup(name='tfw',
+setup(
+    name = 'tfw',
     version = version,
     description = 'Avatao tutorial-framework',
     url = 'https://github.com/avatao-content/baseimage-tutorial-framework',
@@ -20,4 +20,10 @@ setup(name='tfw',
     packages = find_packages('lib'),
     package_dir = {'': 'lib'},
     install_requires = requirements,
-      zip_safe=False)
+    extras_require = {
+        'docs': [
+            'sphinx >= 1.7.0',
+        ],
+    },
+    zip_safe = False,
+)