Add OHF logo to README (home-assistant#3074)

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## Summary
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Adds the OHF badge to the README

## Screenshots
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## Link to pull request in Documentation repository
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Documentation: home-assistant/companion.home-assistant#

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Author: mrdarrengriffin

README.md

@@ -128,3 +128,5 @@ Apache-2.0
 ## Credits
 
 The format and some content of this README.md comes from the [SwipeIt](https://github.com/ivanbruel/SwipeIt) project.
+
+[![Home Assistant - A project from the Open Home Foundation](https://www.openhomefoundation.org/badges/home-assistant.png)](https://www.openhomefoundation.org/)