[clang] [Clang][analyzer] add documentation for optin performance padding (padding checker) #73675 (PR #86411)

[Balazs Benics via cfe-commits]

https://github.com/steakhal requested changes to this pull request.

The docs should also explain why is a problem to have padding bytes, and how to fix it.

How does the generated html look like after your change for this file?
(Have a look at my commits to this or to the releasenotes file for clang to see what commands to run to generate it)

Does the checker have any limitations? Why is it even implemented in CSA?

https://github.com/llvm/llvm-project/pull/86411