release note

Author: el-ev

llvm/docs/ReleaseNotes.md

@@ -186,6 +186,8 @@ Changes to the RISC-V Backend
 * Adds assembler support for the Andes `XAndesperf` (Andes Performance extension).
 * `-mcpu=sifive-p870` was added.
 * Adds assembler support for the Andes `XAndesvpackfph` (Andes Vector Packed FP16 extension).
+* Adds assembler support for the standard `Q` (Quad-Precision Floating Point) 
+  extension.
 
 Changes to the WebAssembly Backend
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