Update CHANGELOG to match release branches 6.2 and 6.3 (#1391)

* [CHANGELOG] Add Known issues for ROCm 6.2.1

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

* Updated 6.2.1 known issues to match the content in develop.

* Updated CHANGELOG for ROCm 6.3 release. (#1380)

* Updated CHANGELOG for ROCm 6.3 release.

* Update CHANGELOG to new format.

Co-authored-by: Jeffrey Novotny <jnovotny@amd.com>

---------

Co-authored-by: Jeffrey Novotny <jnovotny@amd.com>

---------

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

CHANGELOG.md

@@ -2,19 +2,42 @@
 
 Full documentation for RCCL is available at [https://rccl.readthedocs.io](https://rccl.readthedocs.io)
 
+## RCCL 2.21.5 for ROCm 6.3.0
+
+### Added
+
+* MSCCL++ integration for specific contexts
+* Performance collection to rccl_replayer
+* Tuner Plugin example for MI300
+* Tuning table for large number of nodes
+* Support for amdclang++
+* New Rome model
+
+### Changed
+
+* Compatibility with NCCL 2.21.5
+* Increased channel count for MI300X multi-node
+* Enabled MSCCL for single-process multi-threaded contexts
+* Enabled gfx12
+* Enabled CPX mode for MI300X
+* Enabled tracing with rocprof
+* Improved version reporting
+* Enabled GDRDMA for Linux kernel 6.4.0+
+
+### Resolved issues
+
+* Fixed model matching with PXN enable
+
 ## RCCL 2.20.5 for ROCm 6.2.1
-
+### Fixed
+- GDR support flag now set with DMABUF
 ### Known issues
+- On systems running Linux kernel 6.8.0, such as Ubuntu 24.04, Direct Memory Access (DMA) transfers between the GPU and NIC are disabled and impacts multi-node RCCL performance.
+  - This issue was reproduced with RCCL 2.20.5 (ROCm 6.2.0 and 6.2.1) on systems with Broadcom Thor-2 NICs and affects other systems with RoCE networks using Linux 6.8.0 or newer.
+  - Older RCCL versions are also impacted.
+  - This issue will be addressed in a future ROCm release.
 
-On systems running Linux kernel 6.8.0, such as Ubuntu 24.04, Direct Memory Access (DMA) transfers between the GPU and NIC are disabled and impacts multi-node RCCL performance.
-
-This issue was reproduced with RCCL 2.20.5 (ROCm 6.2.0 and 6.2.1) on systems with Broadcom Thor-2 NICs and affects other systems with RoCE networks using Linux 6.8.0 or newer.
-
-Older RCCL versions are also impacted.
-
-This issue will be addressed in a future ROCm release.
-
-## Unreleased - RCCL 2.20.5 for ROCm 6.2.0
+## RCCL 2.20.5 for ROCm 6.2.0
 ### Changed
 - Compatibility with NCCL 2.20.5
 - Compatibility with NCCL 2.19.4