Simplify process to restart GetTor

Right now our Survival Guide says that to restart GetTor, one simply needs to run /home/gettor/gettor/bin/gettor_service \[start|restart\], however this actually needs to be run from where the gettor repository is checked out in order to actually work because it uses relative paths:

case "$1" in
start)
   twistd3 --python=scripts/gettor --logfile=log/gettor.log --pidfile=gettor.pid

This has caused some confusion (for example in #77 (closed)) so we should alter how we do this. BridgeDB "solves" this slightly differently by defining the production environment in a separate bridgedb-admin repository.

I'm not sure we want to do that here, and I'm also not sure what https://gitlab.torproject.org/tpo/anti-censorship/gettor-project/gettor-ansible is for.