[Manual] Add some information about sub-domain rules
https://www.torproject.org/docs/tor-manual.html.en
HIDDEN SERVICE OPTIONS The following options are used to configure a hidden service.
We need official statement about second-level domain(subdomain) of .onion. Likely,
this one(1) and, git.xxxxxxxxx.onion are using second level domain. I know only two URLs.
1: https://tor.stackexchange.com/questions/10068/sub-domain-of-onion-is-allowed-officialy