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

[Nicolas van Kempen via cfe-commits]

nicovank wrote:

![image](https://github.com/user-attachments/assets/a40849e3-435c-4812-8aa0-3fa9ba5b6c5d)

Looks like you have the "private email" setting enabled on GitHub, [I believe LLVM policy is to discourage it](https://discourse.llvm.org/t/hidden-emails-on-github-should-we-do-something-about-it/74223/73). Could you please uncheck the private email box at https://github.com/settings/emails?

Hopefully this is enough to fix it, you might also have to squash and rebase commits, let's see. Thanks!

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