Document the toolchain transition and add notes about toolchain behavior with configuration.
Document the toolchain transition and add notes about toolchain behavior with configuration.

PiperOrigin-RevId: 423898586

cushon/bazel,bazelbuild/bazel,katre/bazel,katre/bazel,cushon/bazel,bazelbuild/bazel,cushon/bazel,ButterflyNetwork/bazel,cushon/bazel,bazelbuild/bazel,ButterflyNetwork/bazel,cushon/bazel,katre/bazel,bazelbuild/bazel,katre/bazel,bazelbuild/bazel,ButterflyNetwork/bazel,bazelbuild/bazel,ButterflyNetwork/bazel,ButterflyNetwork/bazel,cushon/bazel,ButterflyNetwork/bazel,katre/bazel,katre/bazel