github-pages-tutorial: Add git-commit-filetree instructions

[0cjs]

The git-commit-filetree program replaces seven error-prone commands in the release process with a single, simple command. As a bonus, it also doesn't need a special rsync command to remove old files deleted from the source.

This adds instructions for the use of git-commit-filetree as an alternative to the manual process currently described in the tutorial. The manual process documentation is still maintained, in case people either don't want to use git-commit-filetree or they want to better understand the process.

Testing of the new documentation was done manually, with cut-and-paste of the commands from the rendered document.