[llvm] Add RISC-V support information to readme (PR #132699)

[via llvm-commits]

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@@ -34,8 +34,8 @@ SUPPORTED PLATFORMS
 -------------------
 
 :program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM
-(AArch64 only, snippet generation is sparse), MIPS, and PowerPC (PowerPC64LE
-only) on Linux for benchmarking. Not all benchmarking functionality is
+(AArch64 only, snippet generation is sparse), MIPS, PowerPC (PowerPC64LE
+only) and RISC-V (RV64I/E and RV32I/E) on Linux for benchmarking. Not all benchmarking functionality is
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AnastasiyaChernikova wrote:

Addressed

https://github.com/llvm/llvm-project/pull/132699