[compiler-rt] lsan: Document that ptrace_scope needs to be disabled. (PR #202838)

[Peter Collingbourne via llvm-commits]

pcc wrote:

> Has something changed? I see this on my workstation.

I suspect that it was caused by some package upgrade. I asked @nico to check which packages were upgraded recently on his bot.

https://github.com/llvm/llvm-project/pull/202838