Add link to new website and brief description

[bschilder]

@missyQWQ made a much improved website for the rare disease celltyping project. Once she launches it publicy via Imperial's web hosting services, I can add the link and a brief description to the manuscript.

@missyQWQ could you give us an approximate timeline of when you think this will be ready? We don't need to have all the bells and whistles done right this moment, just a working version. Thanks!