Mention simple-entity type in entities.markdown

[karwosts]

Describe how simple-entity type can be used to get a read only version of a helper in an entities card.

I've seen this question for how to do this come up several times on discord, and the solution is currently undocumented.

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.

Additional information

• Link to parent pull request in the codebase:
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue: fixes #

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]

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[c0ffeeca7]

ah, sorry about that one. I deleted that by mistake.

[c0ffeeca7]

LGTM, thank you, @karwosts 👍