[clang] [BoundsSafety] Initial documentation for -fbounds-safety (PR #70749)

[Dan Liew via cfe-commits]

https://github.com/delcypher approved this pull request.

I have a few minor nits but other than that LGTM.

Please make sure this builds without errors/warnings.

I think you can configure CMake with `-DLLVM_BUILD_DOCS=ON -D LLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERROR=ON` to enable building the documentation. The target to build the docs is `docs-clang-html`

https://github.com/llvm/llvm-project/pull/70749