[llvm] [Offload] Add Offload API Sphinx documentation (PR #147323)

[Ross Brunton via llvm-commits]

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@@ -0,0 +1,21 @@
+.. Offload documentation master file, created by
+   sphinx-quickstart on Fri Jul  4 14:59:13 2025.
+   You can adapt this file completely to your liking, but it should at least
+   contain the root `toctree` directive.
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RossBrunton wrote:

Do we want this "origin" information in the file?

https://github.com/llvm/llvm-project/pull/147323