Update CHANGELOG for ROCm 6.2.x (#1343)

* [CHANGELOG] Update for ROCm 6.2.1

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

* [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.

---------

Signed-off-by: nileshnegi <Nilesh.Negi@amd.com>
Co-authored-by: corey-derochie-amd <161367113+corey-derochie-amd@users.noreply.github.com>

CHANGELOG.md

@@ -2,6 +2,15 @@
 
 Full documentation for RCCL is available at [https://rccl.readthedocs.io](https://rccl.readthedocs.io)
 
+## 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.
+
 ## RCCL 2.20.5 for ROCm 6.2.0
 ### Changed
 - Compatibility with NCCL 2.20.5
@@ -24,12 +33,15 @@ Full documentation for RCCL is available at [https://rccl.readthedocs.io](https:
 - New unit test for main kernel stack size
 - New -n option for topo_expl to override # of nodes
 - Improved debug messages of memory allocations
-- Channel shuffling for IB systems
+- Channel shuffling for multi-node MI300X systems
 ### Fixed
 - Bug when configuring RCCL for only LL128 protocol
 - Scratch memory allocation after API change for MSCCL
 - Incorrect minNchannels in multi-node
-- GDR support flag now set with DMABUF
+
+## RCCL 2.18.6 for ROCm 6.1.2
+### Changed
+- Reduced NCCL_TOPO_MAX_NODES to limit stack usage and avoid overflow
 
 ## RCCL 2.18.6 for ROCm 6.1.0
 ### Changed