review the ENC documentation

See merge request tpo/tpa/wiki-replica!19

 * change the section title to the long form so it is more readable
   from the table of contents (TOC), even if you don't know the
   acronym (which is still included)

 * start by more explicitely saying what we use the ENC for, not how
   it works (which we still keep)

 * try to use the active form more (e.g. "Puppet pulls elements"
   instead of "It can be used by Puppet to define elements")

 * use `code` style for variables

 * be more explicit about role::foo

 * use the more commonly use `tor-puppet.git` root instead of
   `/etc/puppet`, because the latter is not explicit, and might hint
   that users should edit it directly on the server (which is
   definitely not the case)

Experience shows that a single registration token for both shared and
project-locked runners (eg. shadow) works fine. Will add bits about
custom roles for runners in subsequent commit.

spotted in tpo/tpa/team#40432

Related to tpo/tpa/team#40432.

the shim failed to migrated back to chi-node-08: the console was hung,
and shutdown wasn't working either. so advise against that as well.

I got bit by this and tried to send to `?channel=#tpo-admin`, which
obviously fails because # is a special character. Easier to just skip
the pound sign altogether.

chi-node-08 wasn't seeing the disks, presumably because this wasn't
ran.

This actually worked the first time.

This reverts commit 9db505fe.

i hate you markdown, but just now.