Add docs.qir-alliance.org CNAME for QIR Alliance projects

[cgranade]

Several QIR Alliance projects (currently QAT and PyQIR) use GitHub Pages to automatically publish documentation. By default, these docs are published to https://qir-alliance.github.io/, rather than to the official qir-alliance.org domain name. By adding a new CNAME record to the qir-alliance.org domain and a matching CNAME record to the custom domain configuration on GitHub Pages, docs could be published to https://docs.qir-alliance.org/ instead.