Document availability of {{ DEVICE_IP }} and {{ DEVICE_MAC }} in shutdown command section

[invario]

While working on the shutdown section, I noticed you have code implemented to allow substitution in the command for {{ DEVICE_IP }} and {{ DEVICE_MAC }} which I personally find useful and I think other users will too. I think a note here about them would be great, thanks!

[seriousm4x]

Agree, but this requires translations for 21 languages of which I only speak 2. I guess this is where I'd allow AI.

[invario]

PR #1714 pushed :) closed, will resubmit new one

[invario]

New PR #1716 submitted, retained all existing translations and simply added