[clang-tools-extra] [clang-tidy] Improve documentation of bugprone-pointer-arithmetic-on-polymorphic-object (PR #108324)

[Mainak Sil via cfe-commits]

MainakSil wrote:

I have updated the example based on your feedback. The `new`/`delete` usage has been removed to avoid additional undefined behavior. The example now directly passes a pointer to a function, which performs the pointer arithmetic, focusing solely on the issue of undefined behavior in pointer arithmetic on polymorphic objects.

https://github.com/llvm/llvm-project/pull/108324