mkdocs: enable instant loading

This allows text typed into the search box to persist across page navigation, which is
useful when users look up a term but aren't sure on which page they will eventually find
the relevant information. See the [`mkdocs-material` docs][mm-docs] for more
information.

[mm-docs]:
https://squidfunk.github.io/mkdocs-material/setup/setting-up-navigation/#instant-loading

mkdocs.yml

@@ -14,6 +14,7 @@ theme:
     # - navigation.top
     - content.action.edit
     - content.code.copy
+    - navigation.instant
 
   icon:
     repo: fontawesome/brands/github