This CL merges all RBE-specific configuration from .bazelrc_rbe into .bazelrc
so that it will be picked up by default by users running bazel.
It also checks in a bazelrc from the upstream bazel-toolchains repository, and
imports that into our repo-specific .bazelrc. This makes it easier to maintain
and update the bazelrc going forward.
Documentation was added to the README.
PiperOrigin-RevId: 242208733
Change-Id: Iea32de9be85b024bd74f88909b56b2a8ab34851a
Nicolas Lacasse