Add back “Home” link to the “Getting Started” column when the “Home” column isn't mounted (#14707)

* Add back "Home" link to "Getting started" when Home column isn't mounted

* Fix keys in getting_started

It should not matter much in practice as the list of items will only
change extremely rarely, but having a `key` that corresponds to the actual
item makes much more sense than having it be the index of the item within
the list.