use rtd theme instead of default

requirements/base.txt

@@ -1 +1,2 @@
 sphinx
+sphinx_rtd_theme

source/conf.py

@@ -17,6 +17,8 @@ import sys
 import os
 import shlex
 
+import sphinx_rtd_theme
+
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
@@ -111,7 +113,7 @@ todo_include_todos = True
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'alabaster'
+html_theme = "sphinx_rtd_theme"
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
@@ -119,7 +121,7 @@ html_theme = 'alabaster'
 #html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-#html_theme_path = []
+html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".