docs: add sphinx rtd theme

docs/conf.py

@@ -28,7 +28,7 @@
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = ['sphinx.ext.intersphinx', 'sphinx.ext.ifconfig', 'sphinx.ext.todo']
+extensions = ['sphinx.ext.intersphinx', 'sphinx.ext.ifconfig', 'sphinx.ext.todo', 'sphinx_rtd_theme']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -94,7 +94,7 @@
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'default'
+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