[llvm] [Docs] Add documentation for LLVM_ENABLE_CURL (PR #170928)

[Paul Kirth via llvm-commits]

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

LGTM, but you likely want to wait for @mysterymath to confirm, since he's the one that implemented all the debuginfod support in the build.

https://github.com/llvm/llvm-project/pull/170928