Add banner placeholder

index.rst

@@ -6,6 +6,8 @@
 BeagleBoard Documentation
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+.. image:: _static/images/banner.webp
+
 Welcome to the `BeagleBoard project documentation <https://git.beagleboard.org/docs/docs.beagleboard.io>`__.
 If you are looking for help with your Beagle open-hardware development platform, you've found the right place!