Deploy Tor Browser User Manual on Gitlab.com and GitHub pages

At the moment, the Tor Browser User Manual is only accessible on the subdomain: tb-manual.torproject.org. But, thinking about users living in countries that are blocking the torproject.org main domain, they can't access this documentation. Since Lektor is a static generator site, it's possible to host this documentation on gitlab.com and github.com, which aren't censored (in most cases). Example: https://tpoforks.gitlab.io/tor-browser-manual/

Tasks

• Write a CI/CD and deploy this manual on gitlab.com pages. See: team#4 (moved)
• Write Travis-CI or GitHub actions config and deploy this manual on github.com pages. See: Lektor docs

After the tasks above are done, inform users about these mirrors:

• Add TB-manual mirrors on GetTor automatic response
• Add TB-manual mirrors on tb-manual itself
• Add TB-manual mirrors on support.torproject.org entry