docs: add mkdocs material setting (autowarefoundation#2784)

https://squidfunk.github.io/mkdocs-material/setup/setting-up-the-footer/

Signed-off-by: Hayato Mizushima <hayato-m126@users.noreply.github.com>

mkdocs.yaml

@@ -15,6 +15,7 @@ theme:
     - navigation.tabs
     - navigation.tabs.sticky
     - navigation.top
+    - navigation.footer
   favicon: docs/assets/images/autoware-foundation.png
   icon:
     logo: fontawesome/solid/car