6.2 final documentation fixes updated for 6.3 (#1252) (#1399)

* Update CHANGELOG.md

* Update NOTICES.txt

* [DOCS] Note on using less than 8 MI300 GPUs



* Update README.md



---------

Signed-off-by: nileshnegi <Nilesh.Negi@amd.com>
Co-authored-by: nileshnegi <Nilesh.Negi@amd.com>

[ROCm/rccl commit: 8ac63e7e70]

projects/rccl/NOTICES.txt

@@ -1,7 +1,7 @@
 Notices and Licenses file
 _______________________________________________________________
 
-Dependencies on nvidia-nccl v2.17.1-1 (BSD3)
+Dependencies on nvidia-nccl v2.21.5-1 (BSD3)
 
 Copyright (c) 2015-2020, NVIDIA CORPORATION. All rights reserved.
 Modifications Copyright (c) 2019-2023 Advanced Micro Devices, Inc. All rights reserved.