[docs] Updated ReleaseNotes for OpenMP part.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@321561 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ReleaseNotes.rst

@@ -209,7 +209,18 @@ OpenCL C Language Changes in Clang
 OpenMP Support in Clang
 ----------------------------------
 
-...
+- Added options `-f[no]-openmp-simd` that support code emission only foe OpenMP
+  SIMD-based directives, like `#pragma omp simd`, `#pragma omp parallel for simd`
+  etc. The code is emitted only for simd-based part of the combined directives
+  and clauses.
+
+- Added support for almost all target-based directives except for
+  `#pragma omp target teams distribute parallel for [simd]`. Although, please
+  note that `depend` clauses on target-based directives are not supported yet.
+  Clang supports offloading to X86_64, AArch64 and PPC64[LE] devices.
+
+- Added support for `reduction`-based clauses on `task`-based directives from
+  upcoming OpenMP 5.0.
 
 Internal API Changes
 --------------------