[llvm] [dyndbg] Add SHT_LLVM_DYNDBG_ELF to Dynamic Debugging docs (PR #213853)

[Andrew Ng via llvm-commits]

nga888 wrote:

Perhaps also change `"Dynamic Debugging" documentation` to a link to the dynamic debugging docs in the documentation for `SHT_LLVM_DYNDBG_ELF` in `Extensions.md`? i.e. change `"Dynamic Debugging" documentation` -> `` {doc}`DynamicDebugging` ``, I think that should work.

https://github.com/llvm/llvm-project/pull/213853