First of all, what are other people saying about GitHub pages for blogging on it? How many people are using it? Ah, some are not liking it! One person would rather host their own server due to complications.
20180531/DuckDuckGo github pages jekyll blog
20180531/https://gon.to/2015/03/03/f-percent-number-ck-github-pages-for-jekyll-why-i-decided-to-use-digital-ocean/
20180531/https://quorten.github.io
20180531/DuckDuckGo google sitemap.xml
This is an interesting website for automatically generating sitemaps. Alas, it is not necessary as some other sites that are well-indexed yet are still personal blogs do just fine without a sitemap.
20180531/https://www.xml-sitemaps.com
20180531/https://support.google.com/webmasters/answer/156184?hl=en