docs(Combobox): link to an explainer for the two variants of the Combobox
The Combobox Pajamas component page doesn't describe the difference between Combobox, Disclosure and a Listbox. It can be confusing if you haven't visited the Dropdowns page yet. In order to make it more clear this MR adds a link to the Dropdowns page with an explanation of the Combobox variants.