Accecibility notes on navs

Created by: andresgalante

Navs have a section for accessibility notes.

Since most users will just copy and paste the code snippets and hardly anyone will actually read the docs I wonder if we should bake accessibility into every code snippet.

I know it will be way more verbose and it might not show the point of the example, but the dent Bootstrap can make just be changing this would be huge!

@patrickhlauke What do you think? If you like this idea I can work on a PR