I don't understand what "CNAME a specific URL" means. (If you are thinking "can this be done in any reasonable way without GitHub adding the feature", the answe

I don't understand what "CNAME a specific URL" means. (If you are thinking "can this be done in any reasonable way without GitHub adding the feature", the answer is "no": they would have to provide the feature on their end, to provide the right content given the right hostname, the same way many other companies have over the years, including Medium, which is but one of many possible specific examples I mostly bring up as I hear they recently stopped allowing this and it has correctly made people say others should no longer use the platform due to URL lock-in.)