[DOC] Outdated link in README.md

[pauleonix]

Report incorrect documentation

Location of incorrect documentation

rmm/README.md

Line 172 in 1ab4920

[Thrust's CMake documentation](https://github.com/NVIDIA/thrust/blob/main/thrust/cmake/README.md).

Describe the problems or issues found in the documentation
The README still links the archived Thrust repo instead of the new CCCL repo for the Thrust CMake Guide.

Suggested fix for documentation
Replace with https://github.com/NVIDIA/cccl/blob/main/thrust/thrust/cmake/README.md