[LoongArch] Update lld20 release notes

Author: SixWeining

lld/docs/ReleaseNotes.rst

@@ -40,6 +40,8 @@ ELF Improvements
   * ``R_X86_64_CODE_4_GOTTPOFF`` (`#116634 <https://github.com/llvm/llvm-project/pull/116634>`_)
   * ``R_X86_64_CODE_4_GOTPC32_TLSDESC`` (`#116909 <https://github.com/llvm/llvm-project/pull/116909>`_)
   * ``R_X86_64_CODE_6_GOTTPOFF``  (`#117675 <https://github.com/llvm/llvm-project/pull/117675>`_)
+* Supported relocation types for LoongArch target: ``R_LARCH_TLS_{LD,GD,DESC}_PCREL20_S2``.
+  (`#100105 <https://github.com/llvm/llvm-project/pull/100105>`_)
 
 Breaking changes
 ----------------