[llvm] [SPIR-V] Extend SPIRVUsage.rst document (PR #84744)

[Arvind Sudarsanam via llvm-commits]

================
@@ -14,10 +14,13 @@ Introduction
 The SPIR-V target provides code generation for the SPIR-V binary format described
 in  `the official SPIR-V specification <https://www.khronos.org/registry/SPIR-V/>`_.
 
+Usage
----------------
asudarsa wrote:

May be renamed as 'Compiler Options"?

https://github.com/llvm/llvm-project/pull/84744