The extension adds two new directive:
- `cards` is the row container for one or more `card` directives.
- `card` is the implementation of a Bootstrap card that accepts a
`target` argument for the href of the card, a `large` option to render
the card on two columns, and arbitrary content that is shown in the
card body.
task-3141419
This commit also replaces references to the "Building a module"
tutorial by references to the "Getting started" tutorial.
task-2991663
Part-of: odoo/documentation#3629
