make readthedocs available

docs/conf.py

@@ -63,9 +63,11 @@ language = 'zh'
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
-import sphinx_rtd_theme
-html_theme = "sphinx_rtd_theme"
-html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
+on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
+if not on_rtd:
+    import sphinx_rtd_theme
+    html_theme = "sphinx_rtd_theme"
+    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # 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,