Document git use when GitHub is HTML host

[rbeezer]

Moving HTML output to GitHub for a "GitHub Pages" site needs to be done via a git repository. Best practice should be to use a different repository than the one holding source files. While adding this to teh section on hosting, also check the emphasis on not putting HTML output into the same repository as source.

[rbeezer]

See too #798

[rbeezer]

And include the hint: -stringparam debug.datedfiles no

[rbeezer]

Suggest having an experienced git user do the initial setup and loading of the HTML files.