Documentation/llvm: add Chimera Linux, Google and Meta datacenters

Chimera Linux is a Linux distribution from 2021 that builds its kernels
with Clang.

Google transitioned its data center fleet to run Clang built kernels in
2021, and Meta did so as well in 2022.  Meta talked about this at LPC
2022 at a talk titled Kernel Live Patching at Scale.

These were important milestones for building the kernel with Clang.
Making note of them helps improve confidence in the project.

Reviewed-by: Tom Rix <trix@redhat.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
Co-developed-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>