Doc: Clusters from Scratch: Use code-block:: console

Previously used "none" everywhere, based on commit 2cec47fe. However,
"console" appears to work fine. The only undesirable thing I notice is
that it highlights the word "then" as though it's being used in an
if-then-else construct.

Reference:

• https://pygments.org/docs/lexers/#pygments.lexers.shell.BashSessionLexer

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>