Adds documentation for https://github.com/civicrm/civicrm-core/pull/10984

With only one example, a reader might misinterpret the example as saying
that `Search Preferences` has been renamed `domain`.  Including two examples
should more clearly indicate that *all* group-names are now flattened to
just `domain`.

This section documents two distinct changes, but they had different
formatting -- which made it seem that (perhaps) the one code-block was
describing both changes.

This change uses similar formatting for both examples and changes the
indentation/alignment to indicate that they're distinct.

- Conform to standards
- Fix broken links