Document multi-proc method selection for profiling (#23802)

Signed-off-by: jdebache <jdebache@nvidia.com>

docs/contributing/profiling.md

@@ -73,6 +73,8 @@ apt install nsight-systems-cli
 
 ### Example commands and usage
 
+When profiling with `nsys`, it is advisable to set the environment variable `VLLM_WORKER_MULTIPROC_METHOD=spawn`. The default is to use the `fork` method instead of `spawn`. More information on the topic can be found in the [Nsight Systems release notes](https://docs.nvidia.com/nsight-systems/ReleaseNotes/index.html#general-issues).
+
 #### Offline Inference
 
 For basic usage, you can just append `nsys profile -o report.nsys-rep --trace-fork-before-exec=true --cuda-graph-trace=node` before any existing script you would run for offline inference.