Add guidance on breadcrumbs

[timja]

Describe your use-case which is not covered by existing documentation.

How they are generated (ModelObject)

When to use f:breadcrumb-config-outline and f:breadcrumb

or alternatively updating the l:layout API to be more intuitive / adding it automatically when not a ModelObject index page.

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

No response

[daniel-beck]

Ideally it would:

• Explain in detail why it needs to work as documented, or
• Be little different from how things currently work

Just changing things for the sake of changing, or perhaps a tiny improvement, does not seem worth creating lots of work across the plugin ecosystem.