Fix error in setup entry points (#466)

* Fix error in setup entry points

  This was missing from b3225c5

* Add comment about what setup is doing

* Optimize python os import

* Address Review: Remove uses of os.path

Author: Blendify

sphinx_rtd_theme/__init__.py

@@ -3,13 +3,17 @@
 From https://github.com/ryan-roemer/sphinx-bootstrap-theme.
 
 """
-import os
+from os import path
 
 __version__ = '0.2.5b1'
 __version_full__ = __version__
 
 
 def get_html_theme_path():
     """Return list of HTML theme paths."""
-    cur_dir = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+    cur_dir = path.abspath(path.dirname(path.dirname(__file__)))
     return cur_dir
+
+# See http://www.sphinx-doc.org/en/stable/theming.html#distribute-your-theme-as-a-python-package
+def setup(app):
+    app.add_html_theme('sphinx_rtd_theme', path.abspath(path.dirname(__file__)))