docs(tutorial): add pre-v2.3 GIT_SSH example
docs(tutorial): add pre-v2.3 GIT_SSH example

It goes along with the new one advertising the GIT_SSH_COMMAND
environment variable.

Related to #256

manasdk/GitPython,cdht/GitPython,StyXman/GitPython,h4ck3rm1k3/GitPython,beni55/GitPython,gitpython-developers/gitpython,jeblair/GitPython,roidelapluie/GitPython,gitpython-developers/GitPython,avinassh/GitPython,cdht/GitPython,pengshp/GitPython,roidelapluie/GitPython,zsjohny/GitPython,manasdk/GitPython,bwrsandman/GitPython,bwrsandman/GitPython,gitpython-developers/GitPython,cdht/GitPython,pengshp/GitPython,StyXman/GitPython,gitpython-developers/gitpython,ghtdak/GitPython,avinassh/GitPython,expobrain/GitPython,zsjohny/GitPython,breavo/GitPython,StyXman/GitPython,dpursehouse/GitPython,nvie/GitPython,pengshp/GitPython,zsjohny/GitPython,expobrain/GitPython,jeblair/GitPython,bwrsandman/GitPython,dpursehouse/GitPython,ghtdak/GitPython,nvie/GitPython,beni55/GitPython,h4ck3rm1k3/GitPython,breavo/GitPython,avinassh/GitPython