Add a 'back-to-top' button

See https://squidfunk.github.io/mkdocs-material/setup/setting-up-navigation/?h=back+to+top#back-to-top-button

Author: cmitu

mkdocs.yml

@@ -27,6 +27,8 @@ theme:
   language: 'en'
   logo: 'images/logo.png'
   favicon: 'images/logo.png'
+  features:
+    - navigation.top
   palette:
     - media: "(prefers-color-scheme: light)"
       scheme: default