[llvm] [Offload][Conformance] Add README file (PR #155190)

[Leandro Lacerda via llvm-commits]

leandrolcampos wrote:

> Most of this is documentation, I'd prefer that go with the `libc` documentation somewhere. Maybe @lntue knows a good place for that to live. Building instructions should link to offload / libc. This should probably just be a description of how to run the tests.

Thanks for the feedback! I've already pushed an update to address your point about the build instructions. The "Getting Started" section now links to the official libc for GPUs documentation.

https://github.com/llvm/llvm-project/pull/155190