Documentation: templates for documentation pages

At the moment we don't have any standard for documentation pages.

It would be good if we at least had templates for chip family pages (`Documentation/platforms///index.rst>`) and board pages (`Documentation/platforms//boards//index.rst>`) in Supported Platforms.

Example from Zephyr: https://github.com/zephyrproject-rtos/zephyr/blob/main/doc/templates/board.tmpl

The basic template for `/drivers` showing the minimum that should be included also seems quite reasonable.