Add documentation for installation on older BIOS's which don't detect…

[tsvi]

… the EFI entry correctly

Fixes home-assistant/operating-system#1760

Proposed change

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

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• This PR fixes or closes issue: fixes #

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• This PR uses the correct branch, based on one of the following:
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[probot-home-assistant]

It seems that this PR is targeted against an incorrect branch since it has a parent PR on one of our codebases. Documentation that needs to be updated for an upcoming release should target the next branch. Please change the target branch of this PR to next and rebase if needed.
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[agners]

It makes sense to add this as some systems indeed require it to be able to boot HAOS 👍

[frenck]

Thanks, @tsvi 👍