build: disable jekyll

Add .nojekyll to disable jekyll on Github pages.
See https://docs.github.com/en/pages/getting-started-with-github-pages/creating-a-github-pages-site?versionId=free-pro-team%40latest&productId=pages&restPage=getting-started-with-github-pages%2Cconfiguring-a-publishing-source-for-your-github-pages-site#static-site-generators

This should allow the .well-known directory be served.

Author: leejuyuu