add Test Hub page

[emiltin]

page with

• what is the test hub
• how do we test equipment
• results
• how to get your equipment included

A first easy step is to show GitHub action badges, as we do in the readme here: https://github.com/rsmp-nordic/rsmp_validator#test-hub

A badge is just a link to an SVG file, that you can insert in markdown (or raw html):

[emiltin]

initial page added at https://rsmp-nordic.org/compliance/