This makes us less dependent on alberti's name, but also could trigger
non-root SSH config rules, because it's not necessary here.

it's trivial, but if we don't say so, people might miss it...

At the time of writing, we have the following ways of creating a
filesystem in the wiki:

    anarcat@curie:help.torproject.org(master)$ git grep mkfs
    howto/ganeti.md:        mkfs /dev/vg_ganeti/srv-tmp &&
    howto/ganeti.md:        mkfs /dev/vg_ganeti/srv &&
    howto/lvm.md:    mkfs -t ext4 /dev/vg_ganeti/srv
    howto/new-machine-cymru.md:    mkfs.ext4 -j /dev/mapper/36782bcb00063c6a500000aa36036318d
    old/new-kvm-virsh-vm.md:mkfs.ext4 "$part1"
    service/ci.md:        mkfs -t ext4 -j /dev/sdc

Most of them use `-t ext4` instead of `.ext4`. I consider that to be
best practice, because it doesn't assume implementation
details (e.g. the existence of `mkfs.ext4`) in `mkfs`.

We especially do not, ever, use `-m` in the filesystem creation, let
alone with "zero percent". That feels like a bad idea in general: if
we run out of disk space, we have no emergency procedure to
recover. We should definitely avoid that: in some cases, we *may* want
to reduce the percentage from the default (5%) to something
smaller (say 1%, it even supports fractional percentages).

We should probably *always* use a journal as well, although by
default (in `mke2fs.conf`) the journal is enabled by
default (`has_journal`) is set, so it is really redundant nowadays.

address editor's feedback on dangerzone documentation

Closes team#40293

See merge request !14

This shows more clearly that nagios and DNSWL can happen in the
backgroun.

We expand on what sanitization means in the guidelines below instead
of making the steps more complicated.

... and *definitely* not the *rejected* ones!

When doing the install today, I thought the "hostname has been set"
step implied the other so, obviously, they belong together.