make readthedocs available

docs/conf.py

@@ -63,12 +63,16 @@ language = 'zh'
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
+# on_rtd is whether we are on readthedocs.org, this line of code grabbed from docs.readthedocs.org
 on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
-if not on_rtd:
+
+if not on_rtd:  # only import and set the theme if we're building docs locally
     import sphinx_rtd_theme
-    html_theme = "sphinx_rtd_theme"
+    html_theme = 'sphinx_rtd_theme'
     html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
+# otherwise, readthedocs.org uses their theme by default, so no need to specify it
+
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".