Add GitHub Pages repo for org root

[cgranade]

At the moment, GitHub Pages content published by member repositories is made available at https://qir-alliance.github.io/, but visiting the domain root at https://qir-alliance.github.io results in a 404, inadvertently communicating that the qir-alliance.github.io domain does not exist. To address this, it would be great to add a new repo at qir-alliance/qir-alliance.github.io whose GitHub Pages content is a simple website (e.g.: Jekyll or 11ty.js) with content replicated from .github/README.md. In the future, that could also provide a place to publish blog posts and other QIR Alliance content that does not neatly fit into any particular member repository.