[llvm] [llvm-link] Add more detail to `--internalize` description (PR #170397)

[Nikita Popov via llvm-commits]

nikic wrote:

I'd suggest adding more detailed documentation to the man page (https://github.com/llvm/llvm-project/blob/main/llvm/docs/CommandGuide/llvm-link.rst) rather than the option description.

https://github.com/llvm/llvm-project/pull/170397