[llvm] [SandboxIR][Doc] Add a Doc file for Sandbox IR (PR #98691)

[via llvm-commits]

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@@ -288,3 +290,6 @@ Additional Topics
 
 :doc:`RISCV/RISCVVectorExtension`
    This document describes how the RISC-V Vector extension can be expressed in LLVM IR and how code is generated for it in the backend.
+
+:doc:`Sandbox IR <SandboxIR>`
+   Describes the design and usage of Sandbox IR, a transactional layer over LLVM IR.
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vporpo wrote:

Done

https://github.com/llvm/llvm-project/pull/98691