Add power command to System Bridge docs

[timmo001]

Proposed change

For home-assistant/core#95719

Type of change

• Added documentation for a new feature I'm adding to Home Assistant (next branch).

Additional information

• Link to parent pull request in the codebase: Add power service to System Bridge integration core#95719

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

Learn more about our pull request process.

[frenck]

Thanks, @timmo001 👍

../Frenck

Comment addressed